Yugoslavia was a state concept among the South Slavic intelligentsia and later popular masses from the 19th to early 20th centuries that culminated in its realization after the 1918 collapse of Austria-Hungary at the end of World War I and the formation of the Kingdom of Serbs, Croats and Slovenes. However, from as early as 1922 onward, the kingdom was better known colloquially as Yugoslavia (or similar variants); in 1929 the name was made official when the country was formally renamed the "Kingdom of Yugoslavia".

The creation of Yugoslavia has been described as expansionist and irredentist in its approach to foreign policy, and federalist in its approach to politics, with power centralised in the Serb-dominated government. Despite the idea of Yugoslavism having promoted equality among the South Slavic ethnic groups, the new Yugoslav state was ruled by the Serbian Karađorđević dynasty that sought to implement pro-Serb policies throughout the country, leaving minority groups like Croatians and Bosniaks (Bosnian Muslims) not feeling represented in the new government. This led to the formation of opposition parties that became identified with particular ethnic groups within the country. Similarly, the concept of Yugoslavism became associated with the idea of a South Slavic nation dominated by Serbs; and in some instances, forced cultural assimilation policies introduced by the Serb-led Yugoslav government. However, the creation of Yugoslavia remained popular even among non-Serbs, as it was seen as a means of unification for South Slavs to protect themselves against non-Slavic powers such as Fascist Italy.

The idea of South Slavic unity was first developed in Habsburg Croatia by a group of Croatian intellectuals led by Ljudevit Gaj in the 1830s, proposing differing levels of cultural and political cooperation and formations. In the first half of the 19th century, this Illyrian movement held that the South Slavs could unite around a shared origin, variants of a shared language, and the natural right to live in their own polity.

To counter Germanization and the territorial domination of Austria-Hungary in the South Slav territories, intellectuals pointed to unification as a solution.

Following the Revolutions of 1848, the Illyrian movement split into those who advocated for Croatian nationalism and those who advocated for Yugoslavism.

In 1848, a plan was created for the creation of a South Slavic Federation. The plan initiated by the Serbian government was made up of the members of the Secret Belgrade Circle, among whom there were people close to the ruling circles.

In the 1860s, within the framework of efforts by Prince Mihailo Obrenović to establish an anti-Ottoman coalition, Roman Catholic bishop Josip Juraj Strossmayer and Serbian Foreign Minister Ilija Garašanin, agreed to work towards establishing a Yugoslav state independent of Austria and the Ottomans.

Further Yugoslav ideals were forged by the Polish and other Western Slavic emigrants in the West who saw that a Russo-Austrian division of the Ottoman Empire must be prevented at all costs and a common state of all South Slavs forged. Czech envoy Frantisek Zach went to Belgrade with a drafted plan the "Načertanije", which called for the unification by Serbia of the South Slav lands as a basis for Serbian resistance to both Russian and Austrian influence.