World War II in the Kingdom of Yugoslavia began on 6 April 1941, when the country was invaded and swiftly conquered by Axis forces and partitioned among Germany, Italy, Hungary, Bulgaria and their client regimes. Shortly after Germany attacked the USSR on 22 June 1941, the Comintern issued directives to all communist parties to come to the Soviet Union's aid, following which the communist-led Yugoslav Partisans launched a guerrilla liberation war fighting against the Axis forces and their locally established puppet regimes, including the Axis-allied Independent State of Croatia (NDH) and the Government of National Salvation in the German-occupied territory of Serbia. This was dubbed the National Liberation War and Socialist Revolution in post-war Yugoslav communist historiography. Simultaneously, a multi-side civil war was waged between the Yugoslav communist Partisans, the Serbian royalist Chetniks, the Axis-allied Croatian Ustaše and Home Guard, Serbian Volunteer Corps and State Guard, Slovene Home Guard, as well as Nazi-allied Russian Protective Corps troops. Both the Yugoslav Partisans and the Chetnik movement initially resisted the Axis invasion. However, after 1941, Chetniks extensively and systematically collaborated with the Italian occupation forces until the Italian capitulation, and thereon also with German and Ustaše forces. The Axis mounted a series of offensives intended to destroy the Partisans, coming close to doing so in the Battles of Neretva and Sutjeska in the spring and summer of 1943. Despite the setbacks, the Partisans remained a credible fighting force, with their organisation gaining recognition from the Western Allies at the Tehran Conference and laying the foundations for the post-war Yugoslav socialist state. With support in logistics and air power from the Western Allies, and Soviet ground troops in the Belgrade offensive, the Partisans eventually gained control of the entire country and of the border regions of Trieste and Carinthia. The victorious Partisans established the Federal People's Republic of Yugoslavia. The conflict in Yugoslavia had one of the highest death tolls by population in the war, and is usually estimated at around one million, about half of whom were civilians. Genocide and ethnic cleansing was carried out by the Axis forces (particularly the Wehrmacht) and their collaborators (particularly the Ustaše and Chetniks), and reprisal actions from the Partisans became more frequent towards the end of the war, and continued after it.
== Background == Prior to the outbreak of war, the government of Milan Stojadinović (1935–1939) tried to navigate between the Axis powers and the imperial powers by seeking neutral status, signing a non-aggression treaty with Italy and extending its treaty of friendship with France. At the same time, the country was destabilized by internal tensions, as Croatian leaders demanded a greater level of autonomy. Stojadinović was sacked by the regent Prince Paul in 1939 and replaced by Dragiša Cvetković, who negotiated a compromise with Croatian leader Vladko Maček in 1939, resulting in the formation of the Banovina of Croatia. However, rather than reducing tensions, the agreement only reinforced the crisis in the country's governance. Groups from both sides of the political spectrum were not satisfied: the pro-fascist Ustaše sought an independent Croatia allied with the Axis; Serbian public and military circles preferred alliance with Britain and France, while the then-banned Communist Party of Yugoslavia saw the Soviet Union as a natural ally. Following the fall of France in June 1940, Yugoslavia's Regent Prince Paul and his government saw no way of saving the Kingdom of Yugoslavia except through accommodation with the Axis powers. Although Germany's Adolf Hitler was not particularly interested in creating another front in the Balkans, and Yugoslavia itself remained at peace during the first year of the war, Benito Mussolini's Italy had invaded Albania in April 1939 and launched the rather unsuccessful Italo-Greek War in October 1940. These events resulted in Yugoslavia's geographical isolation from potential Allied support. The government tried to negotiate with the Axis on cooperation with as few concessions as possible, while attempting secret negotiations with the Allies and the Soviet Union, but these moves failed to keep the country out of the war. A secret mission to the U.S., led by the influential Serbian-Jewish Captain David Albala, with the purpose of obtaining funding to buy arms for the expected invasion went nowhere, while the Soviet Union's Joseph Stalin expelled Yugoslav ambassador Milan Gavrilović just one month after agreeing a treaty of friendship with Yugoslavia (prior to 22 June 1941, Nazi Germany and Soviet Russia adhered to the non-aggression pact the parties had signed in August 1939 and in the autumn 1940, Germany and the Soviet Union had been in talks on the USSR's potential accession to the Tripartite Pact).
== 1941 == Under sustained German pressure and following failed attempts to maintain neutrality, Yugoslavia signed the Tripartite Pact on 25 March 1941 in the Vienna Belvedere. The following day, protests broke out in Belgrade against the accession. On 27 March 1941, Air Force general Borivoje Mirković led a group of Serbian Air Force officers in overthrowing the Cvetković government in a military coup. Hitler decided to postpone his invasion of the Soviet Union and demolish the Yugoslav state permanently.
Axis invasion and dismemberment of Yugoslavia
==== The April War ==== On 6 April 1941, following Hitler's Directive No. 25 ordering the military destruction and political dismemberment of Yugoslavia, Germany, Italy, and Hungary invaded the Kingdom of Yugoslavia. Belgrade was bombed by the German Luftwaffe on the same day. The conflict, known as the April War, lasted eleven days, ending with the unconditional surrender signed by General Danilo Kalafatović on 17 April on behalf of the Yugoslav government and army. Approximately 344,000 Yugoslav officers and troops were taken prisoner, roughly half the armed forces. After most Croats and Macedonians were released, between 200,000 and 300,000, mostly Serbs, were transferred to camps in Germany and Italy. A further 300,000, again largely Serbs, escaped capture by disregarding the capitulation order. The early withdrawal of crack German units from Yugoslavia in late April, necessitated by preparations for Operation Barbarossa, prevented the Wehrmacht from fully securing the occupied territory. The Royal Yugoslav Army's arsenal fell into German hands, and King Petar II and his government fled first to Greece and subsequently to London where they established a government-in-exile. The Yugoslav army's resistance was undermined by structural weaknesses in organisation, training, and national cohesion. Mobilisation had been deliberately withheld to avoid provoking Hitler and was not ordered until 3 April. Of roughly 700,000 men under arms, more than 400,000 had fewer than four weeks of training and not one division was at full readiness when the invasion began. The Axis brought 52 divisions: 24 German, 23 Italian, and 5 Hungarian, with 2,200 aircraft; German armoured and motorised formations that were veterans of the Polish, Norwegian and French campaigns led the assault. According to Tomasevich, the insistence of the Yugoslav army on defending all its borders assured its failure from the start. Resistance resolve among the officer corps and general public was greater among Serbs than elsewhere in the country, with fighting resolution running highest in the period around the March 27 coup; once the bombing and invasion began defeatism spread quickly through the higher ranks of the Serbian-dominated officer corps. Elsewhere in the country resolve was present only to a limited degree, with potential fifth column risks among Ustaše sympathisers, pro-Bulgarian population in Macedonia, Albanians in Kosovo, and the Volksdeutsche minority in Vojvodina. According to Matteo J. Milazzo, German units advancing on Zagreb in the first week of fighting were received favourably by much of the Croatian civilian population. Italian military intelligence reported on 12 April 1941, five days before the Yugoslav surrender, that Croatian and Slovene reservists were abandoning their weapons and returning home, with large units falling apart. Historian Aleksa Djilas acknowledges that while some Croatian units deserted, most Croatian officers remained loyal to the Yugoslav army until 10 April when the NDH was proclaimed. Most senior commanders, convinced that resistance was hopeless, focused on surrender rather than continued defence.
==== Partition and occupation ==== With Yugoslav resistance collapsed, Germany proceeded to partition the country in accordance with overlapping strategic interests: incorporating Slovene territory into the Greater Reich, exploiting Serbia's communication lines and mineral resources, rewarding Italy, Hungary and Bulgaria for their roles in the invasion and establishing an independent Croatian state as a reward for the Ustaše. Germany occupied the largest, northern part of Slovenia while Italy annexed the southern part as the Ljubljana Province and Hungary annexed the northeastern Prekmurje region. Slovene political parties had established a Slovene National Council on the first day of the invasion, but it surrendered to the Italian army on 12 April when Italian forces entered Ljubljana. Following the Yugoslav surrender, Germany occupied Serbia outright and placed it under direct military administration, the only territory in dismembered Yugoslavia under direct German military rule, administered first through a Commissioner Administration and then, from 29 August 1941, through a quisling government headed by General Milan Nedić. On 10 April 1941, to coincide with the entry of German troops into Zagreb, Slavko Kvaternik proclaimed the Independent State of Croatia (NDH) on behalf of the Ustaše movement, with German assistance. Its territory extended over much of modern Croatia and all of modern Bosnia and Herzegovina. It functioned as an Italo-German quasi-protectorate, a puppet state, ratified under the Treaties of Rome of 18 May. The NDH was divided by a Line of Demarcation into German and Italian zones with German influence steadily growing at Italy's expense. The state owed its creation and continued existence to the two Axis powers. Italy annexed Kosovo, coastal areas of the Croatian Littoral, large sections of Dalmatia, nearly all of the Adriatic islands, the Bay of Kotor, and gained control over Montenegro. Hungary occupied and subsequently annexed Vojvodina, Baranja, Bačka and Međimurje. The Bulgarian army moved into nearly all of modern North Macedonia and parts of eastern Serbia on 19 April 1941, with Bulgaria formally annexing these territories alongside Greek western Thrace and eastern Macedonia on 14 May. The Yugoslav government-in-exile in London retained recognition from the Allied powers.
Occupation forces
The most numerous local force, apart from the four second-line German Wehrmacht infantry divisions assigned to occupation duties, was the Croatian Home Guard (Hrvatsko domobranstvo) founded in April 1941, a few days after the founding of the NDH. The force was formed with the authorisation of German authorities. The task of the new Croatian armed forces was to defend the new state against both foreign and domestic enemies. The Croatian Home Guard was originally limited to 16 infantry battalions and 2 cavalry squadrons – 16,000 men in total. The original 16 battalions were soon enlarged to 15 infantry regiments of two battalions each between May and June 1941, organised into five divisional commands, some 55,000 enlisted men. Support units included 35 light tanks supplied by Italy, 10 artillery battalions (equipped with captured Royal Yugoslav Army weapons of Czech origin), a cavalry regiment in Zagreb and an independent cavalry battalion at Sarajevo. Two independent motorized infantry battalions were based at Zagreb and Sarajevo respectively. Several regiments of Ustaše militia were also formed at this time, which operated under a separate command structure to, and independently from, the Croatian Home Guard, until late 1944. The Home Guard crushed the Serb revolt in Eastern Herzegovina in June 1941, and in July they fought in Eastern and Western Bosnia. They fought in Eastern Herzegovina again, when Croatian-Dalmatian and Slavonian battalions reinforced local units. The Italian High Command assigned 24 divisions and three coastal brigades to occupation duties in Yugoslavia from 1941. These units were located from Slovenia, Croatia and Dalmatia through to Montenegro and Kosovo. From April 1941 the Ustasha regime enacted racial laws targeting Serbs, Jews and Roma, barring them from public employment, confiscating their property and compelling them to wear identifying insignia. Throughout the spring and summer of 1941 Ustasha militias swept through the countryside, killing thousands of Serbs in Bosnia and Croatia; as the massacres spread, Serbs fled to the mountains and some began to fight back. In August 1941 construction began on the Jasenovac concentration camp complex on the rivers Una and Sava, the largest of a network of camps established across the NDH. By mid-summer the scale of the killings had driven large parts of the Serb population into armed insurrection, to the extent that German and Italian occupation forces feared the early collapse of the NDH state. The German plenipotentiary in Croatia, Edmund Glaise von Horstenau, observed as early as September 1941 that Ustasha anti-Serbian policies had produced the opposite of what was intended, driving Serbs into armed resistance.
Early resistance
Armed resistance began in July 1941, emerging in all parts of Yugoslavia except Macedonia. The two resistance movements that emerged, the royalist Chetniks and the communist-led Partisans, initially found themselves side by side and collaborated to some extent, though from the outset they held entirely different concepts of resistance. The Partisans, led by the Communist Party of Yugoslavia (CPY) under Josip Broz Tito, were dedicated to a pan-Yugoslav state of free and equal nations, while the Chetniks were a royalist force organised around Colonel Dragoljub Mihailović, almost exclusively composed of Serb officers and men who had refused to surrender. Mihailović's strategy was to build strength and postpone armed confrontation until Allied participation was imminent, whereas Tito, acting on Comintern directives, moved immediately to armed action.
==== Partisan uprising ==== At the outset the Partisan forces were small, poorly armed and without infrastructure, though the Communist Party of Yugoslavia brought some significant assets to the resistance. From the early 1930s, numerous future Yugoslav Partisan leaders were trained in Comintern military schools in the Soviet Union, receiving instruction in guerrilla warfare, sabotage and military tactics. A cadre of Spanish Civil War veterans within the party's ranks provided experience of modern guerrilla warfare, while in Slovenia the movement drew on experienced TIGR members, an antifascist organisation that had been fighting since 1927 for the liberation of the Slovene and Croatian Littoral from fascist Italy. The CPY conducted its resistance as a broad multinational antifascist movement, deliberately setting aside the issue of socialist revolution in favour of national and antifascist liberation appeals, enabling non-Communists to join the movement. According to Marko Attila Hoare, the Partisan movement was a genuinely multinational movement, though the roles played by the various Yugoslav nationalities were not equivalent; for the first year of its existence the rank-and-file was overwhelmingly Serb, with Serbs comprising approximately 95 per cent of all Partisans in the territory of the NDH by the end of 1941 despite forming only one third of the population. In Slovenia the Liberation Front of the Slovene People was founded in April 1941 as a broad antifascist coalition, later forming the basis for the Slovene Partisans operating as a distinct component of the Yugoslav resistance. In Macedonia, specific local conditions similarly led to the creation of the separate People's Liberation Army of Macedonia. 22 June 1941 marked the start of the Communist Partisan resistance in occupied Yugoslavia. On that day, following Germany's attack on the Soviet Union, the Comintern issued directives to all communist parties to come to the Soviet Union's aid. In Sisak, about fifteen Croatian communists moved into the nearby forest and founded the 1st Sisak Partisan Detachment, the first antifascist partisan detachment formed in Croatia. The detachment began resistance activities the day after its creation, launching sabotage and diversionary attacks on nearby railway lines, destroying telegraph poles, attacking municipal buildings in surrounding villages, seizing arms and ammunition and creating a Communist propaganda network in Sisak and nearby villages.
The following day, 23 June, the CPY made its decision to launch an armed uprising in Serbia. On 27 June the Supreme Staff of the National Liberation Partisan Units of Yugoslavia was constituted, to be chaired by Josip Broz Tito. On 4 July a formal order to begin the uprising was issued. On 7 July, fighting broke out in the village of Bela Crkva near Krupanj in western Serbia when quisling gendarmerie attempted to disperse a public meeting, killing two gendarmes; within weeks the uprising had acquired mass proportions across Serbia. On 10 August 1941 the Partisans formed the Kopaonik Detachment at Stanulović, establishing a liberated zone in the surrounding villages known as the "Miners' Republic" that survived until 11 September. By the end of 1941 Partisan units in Croatia had approximately 7,000 armed combatants, drawing support primarily from Serb villages and to some extent Croat ones. On 22 December 1941 the Partisan Supreme Staff established the 1st Proletarian Brigade at Rudo in East Bosnia, drawn from Serbian and Montenegrin Partisans; Tito framed its establishment as marking the transition from national liberation to social revolution.
Chetnik organisation
The Chetnik resistance force was organised around a small group of Royal Yugoslav Army officers and men, almost exclusively Serbs, who had refused to accept the capitulation. Their leader, Colonel Draža Mihailović, retreated eastward from Doboj in northern Bosnia and on 13 May 1941 reached the highland of Ravna Gora in western Serbia with only seven officers and twenty four NCOs and men. There they established a headquarters designated the Command of Chetnik Detachments of the Yugoslav Army. Through the summer the movement grew as officers made their way from Belgrade to join him; Tomasevich estimated their total strength in the early autumn at no more than three to four thousand men. Mihailović's movement was, however, one of several competing Chetnik formations: Kosta Pećanac, head of the prewar Chetnik Organisation, controlled bands in southern Serbia but had by late June publicly renounced resistance, moving instead toward open collaboration with the occupation authorities. In August 1941 Mihailović established a Central National Committee drawing on Serbian political and cultural figures to act as a civilian political arm. In September he established contact with the government-in-exile in London and was appointed general and defence secretary.
==== Chetnik–Partisan cooperation and breakdown ==== From August 1941 contacts and cooperation emerged between Chetnik and Partisan detachments in Serbia. By September, Chetnik groups began joining the fighting against the Germans, sometimes in joint operations with the Partisans. On 16 September Hitler issued a directive specifying that one hundred hostages be shot for every German soldier killed and fifty for every soldier wounded. The Partisans had by this point established a liberated zone known as the Republic of Užice, where a captured armaments factory was in full operation. On 19 September Tito and Mihailović met at Struganik near Valjevo; both leaders recognised that their tactical and political differences were irreconcilable, though some minor agreements were reached. In mid-October some 1,700 civilians were shot at Kraljevo and 2,778 men and boys were rounded up and executed at Kragujevac. Mihailović concluded that guerrilla operations of any scale would cost an unsustainable number of Serbian lives and intensified his efforts to disengage from active resistance. By late 1941 some 200,000 Serbian officers and men were prisoners of war in Germany, hundreds of thousands of Serbs were being killed in the NDH and German reprisals in Serbia had cost thousands more lives.
A second meeting at Brajići on 27 October produced deeper disagreement than Struganik. Each side demanded operational control over the other's forces; neither would accept subordination. Tomasevich argues that the fundamental incompatibility between the two movements went beyond tactics: the Chetniks, backed by the government-in-exile, sought to preserve the pre-war political and social order and concluded that the Partisans had to be destroyed; the Partisans in turn viewed the Chetniks as the central force of counterrevolution and concluded that they equally had to be defeated. Each side identified the other as its primary political enemy. On 1–2 November Chetnik forces attacked the Partisan Supreme Headquarters at Užice; the Partisans had been forewarned and repulsed the attack. Simon Trew notes that responsibility for the assault was never satisfactorily established, with the balance of probability suggesting it resulted from an independent initiative by some of Mihailović's unruly commanders. On 11 November Mihailović met a German delegation at Divci; the Germans demanded his unconditional surrender and rejected his offers of cooperation against the Partisans as insincere. Mihailović refused and the meeting ended without result. Walter Roberts concludes that later charges of German-Chetnik collusion in the expulsion of the Partisans from Serbia are not substantiated by the evidence. The two guerilla movements which had broadly collaborated until October had become bitter enemies. On 15 November the BBC announced that Mihailović was commander of the Yugoslav armed forces in the homeland; Stevan Pavlowitch notes that at that moment his resistance was being inflated to legendary proportions in the Allied world. A joint British-Yugoslav SOE mission, landed by submarine on the Montenegrin coast in late September, reached Mihailović's headquarters in late October; all the mission could do was urge him to husband his resources and attempt to mediate between the two movements. The first major counter-insurgency operation began on 25 November, with the 113th Infantry and 342nd Infantry Divisions, aided by elements of four further divisions and Serbian collaborationist forces, targeting guerrilla forces in western Serbia. Appeals by Tito to Mihailović on 27 and 28 November to take joint action went unanswered. The Partisans retreated south into the Sandžak and Italian-occupied territory while the Chetniks dispersed into the hills of Ravna Gora. On 3 December orders were issued to destroy Mihailović's detachments; on 6 December the 342nd Infantry Division overran his headquarters at Ravna Gora and he narrowly escaped capture, disbanding most of his forces and going into hiding in the Rudnik Mountain area. By the end of December Bulgaria had assumed responsibility for an occupation zone in eastern Serbia; on 15 January 1942 the Bulgarian 1st Army, with three infantry divisions, formally transferred to south-eastern Serbia and headquartered at Niš, replacing German divisions needed elsewhere. The Partisan setback in Serbia reflected a combination of Axis material superiority, civilian fear of reprisals, the hardship of winter, and the demoralising effect of the civil war with the Chetniks. The Chetniks had been disbanded and the Partisans, driven out, regrouped in eastern Bosnia as a growing resistance force.
1942
Conflict in eastern Bosnia
At the start of 1942 the two resistance movements remained in open conflict across eastern Bosnia. The Partisans held a foothold in the region but faced significant pressure. Although Chetnik forces dominated much of eastern Bosnia, Italian intelligence recognised that the movement possessed little operational unity: forces under Major Dangić followed the Serbian collaborationist prime minister Nedić rather than Mihailović, while Herzegovinian Chetniks under Jevdević acknowledged Dangić rather than Mihailović directly. The Second Enemy Offensive, comprising German and Croatian operations between January and early February 1942, targeted both insurgent movements; Chetnik commanders Dangić and Todorović advised their units that the offensive was directed only at the Partisans and ordered them to withdraw, letting the Germans pass through their positions and severely weakening the Partisan defence. Despite this the offensive failed to destroy the Partisans, who established a new headquarters at Foča, resumed direct radio contact with the Comintern, and reorganised their movement under a broader national liberation appeal, issuing directives establishing people's committees as the civilian organs of authority in liberated territory.
Chetnik–Italian collaboration in Montenegro
In Montenegro, the Partisans suffered a serious setback following their assault on the Italian garrison at Pljevlja in December 1941, which resulted in over 200 dead and widespread desertions. Partisan terror against suspected opponents further alienated the population, and popular support swung sharply against them. In February and March 1942 two local Montenegrin Chetnik commanders, Colonel Stanišić and Captain Djurišić, concluded non-aggression agreements with Italian divisional commands, receiving arms and supplies in exchange for operations against the Partisans; by the end of May they had driven the Partisans out of the greater part of Montenegro. Davide Rodogno argues that the Italians sought above all to secure Chetnik military support against the Partisans, despite being aware that the Chetniks favoured the British and would likely turn their weapons against the Axis should the opportunity arise; the Chetniks for their part collaborated "for reasons of short-term convenience", aware that the Italians' interest in them would end were the Partisans decisively defeated. Mihailović arrived in Montenegro in June 1942 to find these arrangements already in place and local commanders unwilling to subordinate themselves in practice. General Đukanović, the senior commander of all Montenegrin Chetnik forces, then formalised the arrangement in a general agreement with Italian military governor Pirzio Biroli on 24 July 1942. The extent of Mihailović's control over local commanders has been disputed. Tomasevich argues that his principal commanders acted with his backing. Roberts, by contrast, writes that many local agreements were concluded without Mihailović's prior knowledge and that he opposed formal arrangements because they compromised his standing with the Allies. Pavlowitch similarly argues that commanders such as Đurišić recognised Mihailović's authority only insofar as it coincided with their own local interests.
=== The Third Axis Offensive and the Partisan withdrawal to western Bosnia === Through the spring of 1942 local Chetnik forces staged coups against the communist leadership of Partisan detachments across eastern Bosnia, severely weakening the Partisan position in the region. In late February German and NDH military leaders meeting in Zagreb agreed to launch a joint offensive against the insurgency, planned as a two-phase operation: an initial offensive in eastern Bosnia, to be followed by a second against the Partisan stronghold around Mount Kozara in Bosnian Krajina. Further planning followed at a conference in Opatija in early March, where German, Italian and NDH representatives agreed to concentrate forces in eastern Bosnia under General Bader and initially resolved to ban any negotiated agreements with either Chetniks or Partisans; the treatment of the Chetniks specifically remained unresolved and was taken up again at a later conference in Ljubljana.
The resulting Third Enemy Offensive, launched on 15 April, targeted all insurgents between Sarajevo and the Drina. The Croats ultimately vetoed Italian proposals to involve Bosnian Chetniks in the campaign but temporary accords were concluded to include Herzegovinian Chetniks. General Bader judged the operation a success, crediting the Ustasha Black Legion under Lieutenant-Colonel Jure Francetić with significantly helping the Partisans' expulsion from their positions, though German officials remained convinced that Italian sympathy for the Chetniks had hampered the consolidation of these gains elsewhere in the NDH. By June the Partisans had lost practically all their free territory in eastern Bosnia, Montenegro and Herzegovina; the surviving main force began a long march westward toward western Bosnia at the end of June. The march took place partly through Italian-occupied territory; General Glaise von Horstenau noted in his diary that it proceeded under what he described as the Italians' "benevolent encouragement", as the Partisans were fighting mainly with the Ustasha, Croatian Home Guard and Chetniks rather than Italian forces. Having judged the eastern Bosnian operation complete, German commanders turned to the second phase of their plan. After Partisan forces took the town of Prijedor on 16 May, and following the withdrawal of Italian troops who had failed to retake it, the Kozara Offensive began on 10 June under General Friedrich Stahl, who commanded some 31,000 troops, 11,000 German Wehrmacht personnel, nearly 18,000 Ustasha and Home Guard troops and roughly 2,000 Chetniks, against 3,500 Partisans defending the Kozara mountain area near the Ljubija iron mines. Despite their numerical and material superiority the Axis forces required a month and a half to subdue the area, 1,900 Partisans were killed in the fighting, and some 68,000 Serb civilians of the Kozara region were deported to the camps at Jasenovac and Gradina, of whom 24,488 never returned, while a further 1,590 were sent to forced labour in Germany and 2,774 to Norway. Marko Attila Hoare has characterised the campaign as the most systematic genocide practised against the Serbs of the NDH during the war.
Partisan consolidation
In northwestern Bosnia the Partisans established a powerful base among the Serb population of Bosanska Krajina and drew support from Muslim and Croat sympathisers in the region. Despite their military setbacks, the destruction of weaker units had enabled the Partisans to concentrate committed fighters in elite mobile formations such as the proletarian brigades, giving them an increasing edge in combat. The Partisans also intensified their political organisation, making greater use of political commissars and requiring all new recruits to undergo political instruction. The Ustasha regime's continued persecution of the Serb population drove a growing flow of volunteers toward the Partisans, who were increasingly able to offer the civilian population protection. In a major defeat for Ustasha forces, Partisan units from Bosanska Krajina, Lika and Kordun took Bihać and neighbouring towns on 4 November 1942, in what Enver Redžić described as the Partisans' most serious blow against the Ustasha since the start of the uprising. The victory triggered a rapid expansion of Partisan strength across the region and allowed the movement to establish the so-called Bihać Republic. The Partisans were now established in the heart of the NDH, posing a direct threat to Croatian, Italian and German lines of communication. On 26–27 November the town hosted the first session of the Anti-Fascist Council for the National Liberation of Yugoslavia (AVNOJ), laying the political foundations for a new Yugoslav state. The NDH responded with a sustained propaganda campaign portraying both the Partisans and the Chetniks as instruments of Serbian expansionism, denying any genuine Croatian presence within the Partisan movement and treating AVNOJ's Yugoslav orientation as a direct threat to the NDH's survival. In November 1942, Partisan detachments were officially merged into the National Liberation Army and Partisan Detachments of Yugoslavia (NOV i POJ). The military wing of the movement was further reorganised in this period: thirty-one new brigades were formed between July and December 1942, and on 1 November the first permanent divisions, the 1st and 2nd Proletarian and the 3rd Assault, were established, eventually grouped into the 1st Bosnian and 1st Croatian Corps.
1943
=== Critical Axis offensives === In the first half of 1943 two Axis offensives came close to defeating the Partisans. They are known by their German code names Operation Weiss ('White') and Operation Schwarz ('Black'), as the Battle of Neretva and the Battle of Sutjeska after the rivers in the areas they were fought, or the Fourth and Fifth Enemy Offensive, respectively, according to former Yugoslav historiography. On 7 January 1943, the Bulgarian 1st Army also occupied south-west Serbia. Savage pacification measures reduced Partisan activity appreciably. Bulgarian infantry divisions in the Fifth anti-Partisan Offensive blocked the Partisan escape-route from Montenegro into Serbia and also participated in the Sixth anti-Partisan Offensive in Eastern Bosnia. Negotiations between Germans and Partisans started on 11 March 1943 in Gornji Vakuf, Bosnia. Tito's key officers Vladimir Velebit, Koča Popović and Milovan Đilas brought three proposals, first about an exchange of prisoners, second about the implementation of international law on treatment of prisoners and third about political questions. The delegation expressed concerns about Italian involvement in supplying the Chetnik army and stated that the National Liberation Movement was an independent movement, with no aid from the Soviet Union or the UK. Somewhat later, Đilas and Velebit were brought to Zagreb to continue the negotiations. In the Fourth Enemy Offensive, also known as the Battle of the Neretva or Operation Weiss ('White'), Axis forces pushed Partisan troops to retreat from western Bosnia to northern Herzegovina, culminating in the Partisan retreat over the Neretva river. This took place from January to April, 1943.
The Fifth Enemy Offensive, also known as the Battle of the Sutjeska or Operation Schwarz ('Black'), immediately followed the Fourth Offensive and included a complete encirclement of Partisan forces in southeastern Bosnia and northern Montenegro in May and June 1943.
In that August of my arrival [1943] there were over 30 enemy divisions on the territory of Jugoslavia, as well as a large number of satellite and police formations of Ustashe and Domobrani (military formations of the puppet Croat State), German Sicherheitsdienst, chetniks, Neditch militia, Ljotitch militia, and others. The partisan movement may have counted up to 150,000 fighting men and women (perhaps five per cent women) in close and inextricable co-operation with several million peasants, the people of the country. Partisan numbers were liable to increase rapidly. The Croatian Home Guard reached its maximum size at the end of 1943, when it had 130,000 men. It also included an air force, the Air Force of the Independent State of Croatia (Zrakoplovstvo Nezavisne Države Hrvatske, or ZNDH), the backbone of which was provided by 500 former Royal Yugoslav Air Force officers and 1,600 NCOs with 125 aircraft. By 1943 the ZNDH was 9,775 strong and equipped with 295 aircraft.
Italian capitulation and Allied support for the Partisans
On 8 September 1943, the Italians concluded an armistice with the Allies, leaving 17 divisions stranded in Yugoslavia. All divisional commanders refused to join the Germans. Two Italian infantry divisions joined the Montenegrin Partisans as complete units, while another joined the Albanian Partisans. Other units surrendered to the Germans to face imprisonment in Germany or summary execution. Others surrendered themselves and their arms, ammunition and equipment to Croatian forces or to the Partisans, simply disintegrated, or reached Italy on foot via Trieste or by ship across the Adriatic. The Italian Governorship of Dalmatia was disestablished and the country's possessions were subsequently divided between Germany, which established its Operational Zone of the Adriatic Littoral, and the Independent State of Croatia, which established the new district of Sidraga-Ravni Kotari. The former Italian kingdoms of Albania and of Montenegro were placed under German occupation. On 25 September 1943, the German High Command launched Operation "Istrien", and on October 21 the military operation "Wolkenbruch" with the aim of destroying Partisan units in the Slovene-populated lands, Istria and the Littoral. In that operation 2,500 Istrians were killed among whom were Partisans and civilians including women, children, and elderly. Partisan units which did not withdraw from Istria in time were completely destroyed. German troops, including the SS division "Prinz Eugen", on September 25 began to carry out a plan for the complete destruction of the Partisans in Primorska and Istria. Events in 1943 brought about a change in the attitude of the Allies. The Germans were executing Fall Schwarz (Battle of Sutjeska, the Fifth anti-Partisan offensive), one of a series of offensives aimed at the resistance fighters, when F.W.D. Deakin was sent by the British to gather information. His reports contained two important observations. The first was that the Partisans were courageous and aggressive in battling the German 1st Mountain and 104th Light Division, had suffered significant casualties, and required support. The second observation was that the entire German 1st Mountain Division had transited from the Soviet Union on rail lines through Chetnik-controlled territory. British intercepts (ULTRA) of German message traffic confirmed Chetnik timidity. Even though today many circumstances, facts, and motivations remain unclear, intelligence reports resulted in increased Allied interest in Yugoslavia air operations and shifted policy. The Sixth Enemy Offensive was a series of operations undertaken by the Wehrmacht and the Ustaše after the capitulation of Italy in an attempt to secure the Adriatic coast. It took place in the autumn and winter of 1943/1944. At this point the Partisans were able to win the moral, as well as limited material support of the Western Allies, who until then had supported Mihailović's Chetnik Forces, but were finally convinced of their collaboration by many intelligence-gathering missions dispatched to both sides during the course of the war. In September 1943, at Churchill's request, Brigadier General Fitzroy Maclean was parachuted to Tito's headquarters near Drvar to serve as a permanent, formal liaison to the Partisans. While the Chetniks were still occasionally supplied, the Partisans received the bulk of all future support. When the AVNOJ (the Partisan wartime council in Yugoslavia) was eventually recognized by the Allies, by late 1943, the official recognition of the Partisan Democratic Federal Yugoslavia soon followed. The National Liberation Army of Yugoslavia was recognized by the major Allied powers at the Tehran Conference, when United States agreed to the position of other Allies. The newly recognized Yugoslav government, headed by Prime Minister Tito, was a joint body formed of AVNOJ members and the members of the former government-in-exile in London. The resolution of a fundamental question, whether the new state would remained a monarchy or become a republic, was postponed until the end of the war, as was the status of King Peter II. Subsequent to switching their support to the Partisans, the Allies set up the RAF Balkan Air Force (at the suggestion of Maclean) with the aim to provide increased supplies and tactical air support for Marshal Tito's Partisan forces.
1944
=== Last Axis offensive === In January 1944, Tito's forces unsuccessfully attacked Banja Luka. But, while Tito was forced to withdraw, Mihajlović and his forces were also noted by the Western press for their lack of activity. The Seventh Enemy Offensive was the final Axis attack in western Bosnia in the spring of 1944, which included Operation Rösselsprung (Knight's Leap), an unsuccessful attempt to eliminate Josip Broz Tito personally and annihilate the leadership of the Partisan movement.
=== Partisan growth to domination === Allied aircraft specifically started targeting ZNDH (Air Force of the Independent State of Croatia) and Luftwaffe bases and aircraft for the first time as a result of the Seventh Offensive, including Operation Rösselsprung in late May 1944. Up until then Axis aircraft could fly inland almost at will, as long as they remained at low altitude. Partisan units on the ground frequently complained about enemy aircraft attacking them while hundreds of Allied aircraft flew above at higher altitude. This changed during Rösselsprung as Allied fighter-bombers went low en-masse for the first time, establishing full aerial superiority. Consequently, both the ZNDH and Luftwaffe were forced to limit their operations in clear weather to early morning and late afternoon. The Yugoslav Partisan movement grew to become the largest resistance force in occupied Europe, with 800,000 men organised in 4 field armies. Eventually the Partisans prevailed against all of their opponents as the official army of the newly founded Democratic Federal Yugoslavia (later Socialist Federal Republic of Yugoslavia). In 1944, the Macedonian and Serbian commands made contact in southern Serbia and formed a joint command, which consequently placed the Macedonian Partisans under the direct command of Marshal Tito. The Slovene Partisans also merged with Tito's forces in 1944. On 16 June 1944, the Tito-Šubašić agreement between the Partisans and the Yugoslav Government in exile of Peter II was signed on the island of Vis. This agreement was an attempt to form a new Yugoslav government which would include both the communists and the royalists. It called for a merge of the Partisan Anti-Fascist Council of National Liberation of Yugoslavia (Antifašističko V(ij)eće Narodnog Oslobođenja Jugoslavije, AVNOJ) and the Government in exile. The Tito-Šubašić agreement also called on all Slovenes, Croats, and Serbs to join the Partisans. The Partisans were recognized by the Royal Government as Yugoslavia's regular army. Mihajlović and many Chetniks refused to answer the call. The Chetniks were, however, praised for saving 500 downed Allied pilots in 1944; United States President Harry S. Truman posthumously awarded Mihailović the Legion of Merit for his contribution to the Allied victory.
Allied advances in Romania and Bulgaria
In August 1944 after the Jassy-Kishinev Offensive overwhelmed the front line of Germany's Army Group South Ukraine, King Michael I of Romania staged a coup, Romania quit the war, and the Romanian army was placed under the command of the Red Army. Romanian forces, fighting against Germany, participated in the Prague Offensive. Bulgaria quit as well and, on 10 September, declared war on Germany and its remaining allies. The weak divisions sent by the Axis powers to invade Bulgaria were easily driven back. In Macedonia, the Germans swiftly disarmed the 1st Occupation Corps of 5 divisions and the 5th Army, despite short-lived resistance by the latter. Survivors fought their way back to the old borders of Bulgaria. After the occupation of Bulgaria by the Soviet army, negotiations between Tito and the Bulgarian communist leaders were organised which ultimately resulted in a military alliance between the two. In late September 1944, three Bulgarian armies, some 455,000 strong in total led by General Georgi Marinov Mandjev from Sharkovo, entered Yugoslavia with the strategic task of blocking the German forces withdrawing from Greece. The new Bulgarian People's Army and the Red Army 3rd Ukrainian Front troops were concentrated at the old Bulgarian-Yugoslav border. At the dawn of October 8, they entered Yugoslavia from the south. The First and Fourth Bulgarian Armies invaded Vardar Macedonia, and the Second Army south-eastern Serbia. The First Army then swung north with the Soviet 3rd Ukrainian Front, through eastern Yugoslavia and south-western Hungary, before linking up with the British 8th Army in Austria in May 1945.
Liberation of Belgrade and eastern Yugoslavia
Concurrently, with Allied air support and assistance from the Red Army, the Partisans turned their attention to Central Serbia. The chief objective was to disrupt railroad communications in the valleys of the Vardar and Morava rivers, and prevent Germans from withdrawing their 300,000+ forces from Greece. The Allied air forces sent 1,973 aircraft (mostly from the US 15th Air Force) over Yugoslavia, which discharged over 3,000 tons of bombs. On 17 August 1944, Tito offered an amnesty to all collaborators. On 12 September, Peter II broadcast a message from London, calling upon all Serbs, Croats and Slovenes to "join the National Liberation Army under the leadership of Marshal Tito". The message reportedly had a devastating effect on the morale of the Chetniks, many of which later defected to the Partisans. They were followed by a substantial number of former Croatian Home Guard and Slovene Home Guard troops. In September under the leadership of the new Bulgarian pro-Soviet government, four Bulgarian armies, 455,000 strong in total, were mobilized. By the end of September, the Red Army (3rd Ukrainian Front) troops were concentrated at the Bulgarian-Yugoslav border. In the early October 1944 three Bulgarian armies, consisting of around 340,000 men, together with the Red Army, reentered occupied Yugoslavia and moved from Sofia to Niš, Skopje and Pristina to block the German forces withdrawing from Greece. The Red Army organised the Belgrade Offensive, and took the city on 20 October. The partisans meanwhile attempted to stem the German withdrawal as the German Army Group E abandoned Greece and Albania via Yugoslavia and withdraw to defence lines further north. In September 1944, the allies launched Operation Ratweek, aiming to frustrate German movements through Serbia, Croatia and Slovenia. The British also sent a powerful combat unit launching Operation Floxo (known as 'Floydforce') composing of artillery and engineers which the Partisans were lacking. The Partisans with British artillery were able to stem the Germans and liberated Risan and Podgorica between October and December. By this time the Partisans effectively controlled the entire eastern half of Yugoslavia – Serbia, Macedonia, Montenegro – as well as most of the Dalmatian coast. The Wehrmacht and the forces of the Ustaše-controlled Independent State of Croatia fortified a front in Syrmia that held through the winter of 1944–45 in order to aid the evacuation of Army Group E from the Balkans. To raise the number of Partisan troops Tito again offered the amnesty on 21 November 1944. In November 1944, the units of the Ustaše militia and the Croatian Home Guard were reorganised and combined to form the Army of the Independent State of Croatia.
== 1945 == "Every German unit which could safely evacuate from Yugoslavia might count itself lucky." The Germans continued their retreat. Having lost the easier withdrawal route through Serbia, they fought to hold the Syrmian front in order to secure the more difficult passage through Kosovo, Sandzak and Bosnia. They even scored a series of temporary successes against the People's Liberation Army. They left Mostar on 12 February 1945. They did not leave Sarajevo until 15 April. Sarajevo had assumed a last-moment strategic position as the only remaining withdrawal route and was held at substantial cost. In early March the Germans moved troops from southern Bosnia to support an unsuccessful counter-offensive in Hungary, which enabled the NOV to score some successes by attacking the Germans' weakened positions. Although strengthened by Allied aid, a secure rear and mass conscription in areas under their control, the one-time partisans found it difficult to switch to conventional warfare, particularly in the open country west of Belgrade, where the Germans held their own until mid-April in spite of all of the raw and untrained conscripts the NOV hurled in a bloody war of attrition against the Syrmian Front. On 8 March 1945, a coalition Yugoslav government was formed in Belgrade with Tito as Premier and Ivan Šubašić as foreign minister.
