World War II in Yugoslavia
Military operations in World War II on the territory of Yugoslavia started on 6 April 1941, when the kingdom was swiftly conquered by Axis forces and partitioned between Germany, Italy, Hungary, Bulgaria and client regimes. Subsequently, a guerrilla liberation war was fought against the Axis occupying forces and their locally established puppet regimes, including the Independent State of Croatia and the Government of National Salvation in Serbia, by the Communist-led republican Yugoslav Partisans. Simultaneously, a multi-side civil war was waged between the Partisans, the Serbian royalist Chetniks, Croatian nationalist Ustaše and Home Guard, as well as Slovene Home Guard troops.
Both the Yugoslav Partisans and the Chetnik movement initially resisted the occupation. However, after 1941, Chetniks extensively and systematically collaborated with the Italian occupation forces until the Italian capitulation, and thereon also with German and Ustaše forces. The Axis mounted a series of offensives intended to destroy the Partisans, coming close to doing so in winter and spring of 1943.