in April 1941, the Germans created an Axis puppet state called the Independent State of Croatia (, NDH), governed by the Ustaše. Shortly after its creation, largely spontaneous uprisings began to occur throughout the state, caused by the genocidal policies implemented by the Ustaše against Serbs, Jews and Roma. On 4 July, in the wake of the Axis invasion of the Soviet Union, the Communist Party of Yugoslavia (, KPJ) decided to launch a general uprising against the occupying forces across Yugoslavia, in solidarity with the Soviets, and a full-scale rebellion broke out in Bosnia on 27 July. This included local uprisings in the Bosanska Krajina, which spread across the NDH, but the KPJ organisation was initially swept along in the popular uprisings rather than leading the rebellion. On 29 August, Drenović distinguished himself by planning and leading the capture of Mrkonjić Grad by the rebels, but when the town was recaptured by NDH forces four days later, the KPJ blamed him and his troops, citing their poor discipline and anti-Muslim chauvinism. In September, four battalions of fighters were formed in the Ribnik, Janj and Pliva region. One of these, the 3rd "Petar Kočić" Battalion, was commanded by Drenović who, unlike the other battalion commanders in the region, did not allow the KPJ to appoint political commissars to his companies. Mrkonjić Grad did not have a strong KPJ presence, but was under the sway of the sectarian Serb elite, allowing Drenović to arrest Muslim communists, even confronting senior members of the Partisan leadership in the Bosanska Krajina. On 26 September 1941 at the Partisan conference in Stolice in the German-occupied territory of Serbia, the leadership decided to standardise its military organisation across occupied Yugoslavia. During October and November, three detachments were formed in the Bosanska Krajina from existing units such as the 3rd "Petar Kočić" Battalion, and Drenović was appointed as deputy commander of the 3rd Krajina Detachment responsible for operations in the territory of central Bosnia. The Serbs of this region had strong pro-Chetnik/Serb-chauvinist sympathies. The Chetniks were a loosely-organised Serb-chauvinist guerrilla movement putatively led by Draža Mihailović. Of the 34 companies in the detachment, only 13 had KPJ organisations, only 11 had commanders who were members of the KPJ, and only 18 had a political commissar. Many KPJ activists in the region were Muslims or Croats, not easily accepted by the mass of the rank-and-file who were largely