The primary cause for the rebellion was the policies passed by the occupiers. Constant denationalization, including closing Serbian schools, prohibition of the Serbian language and traditions, and burning of books, and looting, requisition, internment, provoked the population. Romania entering the war in August 1916 awakened hope in the Serbian population of a breakthrough of the Salonika Front, some arming themselves and taking to the forests. Kosta Vojinović began the organization of resistance, and in the summer of 1916 established a band in Leposavić, the core of the future Ibar-Kopaonik Detachment. At the end of September 1916, the Serbian High Command sent Kosta Pećanac, reserve infantry lieutenant and veteran Chetnik vojvoda, by airplane into Toplica. He was given the task to establish a secret resistance organization to be activated when the Allies and the Serbian Army break the Salonika Front and arrive at Skoplje. The peak of Serbian discontent came with the Bulgarian announcement of conscription of local Serbs aged 18-50 for military service. Massive flights to the mountains from Bulgarian recruit commissions began. The first armed conflicts began on 20 February between fleeing conscripts and Bulgarian chases. Pećanac and Vojinović established headquarters on Mount Kopaonik. The decision for this rebellion was taken and on February 21, near the Toplica river the rebellion broke out.

What happened first, Romania entering the war or  Kosta Pećanac being sent to Toplica?
Romania entering the war