During World War II, Yugoslavia's military landscape was marked by complexity and significant internal conflict. Following the Axis invasion in April 1941, the Kingdom of Yugoslavia quickly fell, and the country was subsequently divided and occupied by Germany, Italy, Hungary, and Bulgaria. Despite the swift occupation, resistance movements rapidly formed, most notably the communist Partisans led by Josip Broz Tito and the royalist Chetniks led by Draža Mihailovic. The Partisans, gaining widespread support and recognition from the Allies, engaged in guerrilla warfare against the Axis occupiers and their collaborators, ultimately playing a crucial role in the liberation of Yugoslavia. The internal struggle between the Partisans and Chetniks also shaped the post-war political landscape, with Tito emerging victorious and establishing a socialist federal republic. The Yugoslav resistance was one of the most effective in Europe, contributing significantly to the Allied war effort and the eventual defeat of Axis forces in the region.