Yugoslavia was a nation-state.
Croatia became merged with Serbia and Slovenia to form the nation of Yugoslavia in 1918 . Stateless nation . Some ethnic groups were once a stateless nation that later became a nation state ( for example , the nations of the Balkans such as the Croats , Serbs , Bosniaks , Slovenes , Montenegrins , Kosovars and Macedonians were once part of a multinational state of Yugoslavia . Yugoslavia ( Jugoslavija / Југославија , Jugoslavija , Југославија ) was a country in Southeast Europe during most of the 20th century .