Yugoslavia was a country in Southeast Europe and Central Europe for most of the 20th century. It came into existence after World War I in 1918 under the name of the Kingdom of Serbs, Croats and Slovenes by the merger of the provisional State of Slovenes, Croats and Serbs with the Kingdom of Serbia, and constituted the first union of the South Slavic people as a sovereign state, following centuries in which the region had been part of the Ottoman Empire and Austria-Hungary. Peter I of Serbia was its first sovereign. The kingdom gained international recognition on 13 July 1922 at the Conference of Ambassadors in Paris. The official name of the state was changed to Kingdom of Yugoslavia on 3 October 1929.
Yugoslavia was invaded by the Axis powers on 6 April 1941. In 1943, a Democratic Federal Yugoslavia was proclaimed by the Partisan resistance. In 1944 King Peter II, then living in exile, recognised it as the legitimate government. The monarchy was subsequently abolished in November 1945. Yugoslavia was renamed the Federal People's Republic of Yugoslavia in 1946, when a communist government was established. It acquired the territories of Istria, Rijeka, and Zadar from Italy.