The Chetniks were a Second World War guerrilla group operating where?

The Chetnik Detachments of the Yugoslav Army, commonly known as the Chetniks was a World War II movement in Yugoslavia led by Draža Mihailović, an anti-Axis movement in their long-range goals which engaged in marginal resistance activities for limited periods. They also engaged in tactical or selective collaboration with the occupying forces for almost all of the war.

In April 1941 the Germans, Italians and Hungarians invaded Yugoslavia leading to the swift collapse of the Yugoslav state and the surrender of the Yugoslav army. Many Serb detachments refused to surrender and took to the hills. In the wake of the invasion, the Chetniks were the first of the two resistance movements to be founded. The pre-war Chetnik leader Pećanac soon came to an arrangement with Nedić's collaborationist regime in the Territory of the Military Commander in Serbia. Colonel Draža Mihailović, who was "interested in resisting the occupying powers", set up his headquarters in Ravna Gora and named his group "The Ravna Gora Movement" in order to distinguish it from the Pećanac Chetniks and others calling themselves Chetniks who engaged in collaboration with the Germans. But as the other Chetnik groups acted as adjuncts to the occupation, the word "Chetnik" again became associated with Mihailović's force.