of Communist Party officials from across the country, who sought to organize the resistance against the occupiers, was held in Zagreb. In June 1941, a meeting of the Central Committee of KPJ was also held, at which it was decided to start preparations for the uprising. Operation Barbarossa, the Axis invasion of the Soviet Union, began on 22 June 1941. The extent of support for the Partisan movement varied according to region and nationality, reflecting the existential concerns of the local population and authorities. The first Partisan uprising occurred in Croatia on 22 June 1941, when forty Croatian communists staged an uprising in the Brezovica woods between Sisak and Zagreb, forming the 1st Sisak Partisan Detachment. The first uprising led by Tito occurred two weeks later, in Serbia. The Communist Party of Yugoslavia formally decided to launch an armed uprising on 4 July, a date which was later marked as Fighter's Day – a public holiday in the SFR Yugoslavia. One Žikica Jovanović Španac shot the first bullet of the campaign on 7 July in the Bela Crkva incident. The first Zagreb-Sesvete partisan group was formed in Dubrava in July 1941. In August 1941, 7 Partisan Detachments were formed in Dalmatia with the role of spreading the uprising. On 26 August 1941, 21 members of the 1st Split Partisan Detachment were executed by firing squad after being captured by Italian and Ustaše forces. A number of other partisan units were formed in the summer of 1941, including in Moslavina and Kalnik. An uprising occurred in Serbia during the summer, led by Tito, when the Republic of Užice was created, but it was defeated by the Axis forces by December 1941, and support for the Partisans in Serbia thereafter dropped. It was a different story for Serbs in Axis occupied Croatia who turned to the multi-ethnic Partisans, or the Serb royalist Chetniks. The journalist Tim Judah notes that in the early stage of the war the initial preponderance of Serbs in the Partisans meant in effect a Serbian civil war had broken out. A similar civil war existed within the Croatian national corpus with the competing national narratives provided by the Ustaše and Partisans. In the territory of Bosnia and Herzegovina, the cause of Serb rebellion was the Ustaše policy of genocide, deportations, forced conversions and mass killings of Serbs, as was the case elsewhere in the NDH. Resistance to communist