The Chetniks, formally the Chetnik Detachments of the Yugoslav Army, and also the Yugoslav Army in the Homeland and the Ravna Gora Movement, was a Yugoslav royalist and Serbian nationalist movement and guerrilla force in Axis-occupied Yugoslavia. Although it was not a homogeneous movement, it was led by Draža Mihailović. While it was anti-Axis in its long-term goals and engaged in marginal resistance activities for limited periods, it also engaged in tactical or selective collaboration with Axis forces for almost all of the war. The Chetnik movement adopted a policy of collaboration with regard to the Axis, and engaged in cooperation to one degree or another by both establishing a modus vivendi and operating as "legalised" auxiliary forces under Axis control. Over a period of time, and in different parts of the country, the movement was progressively drawn into collaboration agreements: first with the puppet Government of National Salvation in the German-occupied territory of Serbia, then with the Italians in occupied Dalmatia and Montenegro, with some of the Ustaše forces in northern Bosnia, and, after the Italian capitulation in September 1943, with the Germans directly.

The Kingdom of Yugoslavia was a country in Southeast and Central Europe that existed from 1918 until 1941. From 1918 to 1929, it was officially called the Kingdom of Serbs, Croats, and Slovenes, but the term "Yugoslavia" was its colloquial name due to its origins. The official name of the state was changed to "Kingdom of Yugoslavia" by King Alexander I on 3 October 1929.