Yugoslavia refers to several political entities in the Balkans region which existed between 1919 and 2003. Since that latter date, there is no state that officially uses that name.
The first Yugoslavia, briefly called the Kingdom of Serbs, Croats and Slovenes, was a large multi-ethnic kingdom created by the victorious allies after World War I. For a matter of days in 1941, Yugoslavia was a full fledged member of the Axis. However, after the ruling prince was overthrown, Germany invaded and conquered the country, setting up several puppet states including Croatia and Serbia while annexing other territory.
After the War, Josip Tito, a leader of the resistance movement and a devout Communist, eventually gained control of the country, establishing the Socialist Federal Republic of Yugoslavia. Tito successfully removed Yugoslavia from the Soviet sphere of influence, and for the remainder of his life, Tito successfully kept the various ethnic and religious populations at peace. Upon his death, Yugoslavia disintegrated into several smaller states, with substantial bloodshed. A new Federal Republic of Yugoslavia, a rump state, was established in 1992. In 2003 it discarded the name Yugoslavia and began to call itself the State Union of Serbia and Montenegro, then in 2006 it dissolved into Serbia and Montenegro, two separate states.
What was once Yugoslavia is now divided among seven countries: Serbia, Croatia, Montenegro, Bosnia and Herzegovina, Slovenia, North Macedonia, and Kosovo. As of this writing, there has been no noticeable effort to restore "Yugoslavia" as the name of any functioning political entity.
Yugoslavia remained neutral throughout the war. After the major players in that conflict decided to reach an armistice, Marshal Tito agreed to act as an intermediary, sending Yugoslav ambassadors to the erstwhile capitals of the belligerents, to help finalize the peace terms.
Yugoslavia was abolished by the Germans during World War II, and the fascisticIndependent State of Croatia was given hegemony (under German oversight) over the states that had formed that nation. In 1979, the British were obligated to help the Croatians maintain that hegemony over their Serb subjects in exchange for access to German off-shore oil wells.