After the Yugoslavian army capitulated on April 17, 1941, Yugoslavia was distributed between Germany, Italy, Bulgaria, Hungary and the newly formed puppet states Independent State of Croatia , Independent State of Montenegro and Nedić Serbia . Opposition to these occupation regimes caused the formation of resistance movements, resulting in the Communist Party of Yugoslavia (CPY), then only active in the underground but fast gaining popularity, assuming the role of leading the forces in the Yugoslavian resistance. The CPY as an organisation comprised people from, and drew support from, the whole of Yugoslavia; as such, it represented a single Yugoslav identity.
On November 26, 1942, the Partisan leaders of Yugoslavia convened the first AVNOJ meeting at Bihać, in the northwest of Bosnia, in the hope of gaining political legitimacy. Comprising a committee of both the communist and non-communist Partisan representatives, under Josip Broz Tito, AVNOJ proclaimed support for:
In 1943, Germany mounted offensives to improve its control of Yugoslavia, in anticipation of an Allied invasion of the Balkan Peninsula. The Partisans fought Colonel Draža Mihajlović’s forces, which had attacked the Partisans, and in March, outmaneuvered the German army, and defeated the Četniks in Herzegovina and Montenegro, in the famous battle at the river Neretva. Tito ultimately saved two thirds of his men.
In May, however, Germany, Italy, Bulgaria, Independent State of Croatia Ustasha troops and Serbian Chetnik troops launched a final crushing attack against the Partisans in the Sutjeska Gorge, but the Partisans escaped encirclement. This proved to be a turning point, and when Italy surrendered in September, the Partisans captured Italian arms, gained control of coastal territory, and began receiving supplies from the Allies in Italy.
In its second AVNOJ conference in the Bosnian and Herzegovinian town of Jajce, from November 21 to November 29, 1943, Tito declared AVNOJ to be the superior executive authority. The Decision and the resolutions of the second AVNOJ conference were:
Stalin, the Soviet leader, was enraged when he found out that he was not being informed of the November meeting, and reportedly barred Tito from declaring AVNOJ as a provisional government. The Western Allies, however, were not alarmed, because they knew that the Partisans were the only Yugoslav resistance group actively fighting the Germans.
In December 1943, Roosevelt, Churchill, and Stalin decided to support the Partisans. The United Kingdom joined a month later, and stopped supplying the Chetniks. The first Soviet mission arrived at Partisan headquarters, shortly thereafter. The United States kept a military mission with Mihajlović to encourage continued Chetnik aid for downed American fliers.
In May 1944, German airborne forces attacked Tito's headquarters in Drvar, nearly capturing him. Tito fled to Italy, and established a new headquarters on the Adriatic island of Vis. After throwing its full support to the Partisans, Britain worked to reconcile Tito and Petar. At Britain's urging, Petar agreed to remain outside Yugoslavia, and in September, summoned all Yugoslavs to back the Partisans.