Interwar period

At the time of creation of Yugoslavia during the Paris Peace Conference following the conclusion of World War I, the Entente Powers signed the Treaty of Trianon with Hungary after the breakup of Austria-Hungary. Among other things, the treaty defined the border between Hungary and the newly created Kingdom of Serbs, Croats and Slovenes (renamed the Kingdom of Yugoslavia in 1929). Sizable numbers of Hungarians and Volksdeutsche remained in the areas incorporated into the kingdom. The newly formed Kingdom of Yugoslavia was a status quo state which sought to consolidate success of the South Slavic unification movement while Hungary was revisionist state whose leaders believed that their country had a right to some parts of Yugoslavia.

On 14 March 1941 in Budapest Foreign Ministers Aleksandar Cincar-Marković and László Bárdossy signed the Treaty of Eternal Friendship between Yugoslavia and Hungary. Following the short-lasting Yugoslav accession to the Tripartite Pact on 25 March 1941 the Yugoslav coup d'état took place on 27 March 1941 when the regency led by Prince Paul of Yugoslavia was overthrown and King Peter II fully assumed power. The coup led directly to the German-led Axis invasion of Yugoslavia in which Pál Teleki government of Hungary was pressured to join the attack. When Teleki received a call that is thought to have informed him that the German army had just started its march into Hungary.^[1] Teleki committed suicide with a pistol during the night of 3 April 1941 and was found the next morning. His suicide note said in part:

We broke our word, – out of cowardice [...] The nation feels it, and we have thrown away its honor. We have allied ourselves to scoundrels [...] We will become body-snatchers! A nation of trash. I did not hold you back. I am guilty"^[2][3]

Winston Churchill later wrote, "His suicide was a sacrifice to absolve himself and his people from guilt in the German attack on Yugoslavia."^[4] On 6 April 1941, Germany launched Operation Punishment (Unternehmen Strafgericht), the bombing of Belgrade, Yugoslavia. Some historians consider Teleki's suicide an act of patriotism.^[5] Britain shortly afterward broke diplomatic relations with Hungary but did not declare war until December.

World War II

During the World War II in Yugoslavia, Hungarian occupation of Yugoslav territories included military occupation, then annexation, of the Bačka, Baranja, Međimurje and Prekmurje regions of the Kingdom of Yugoslavia.

Cold War

After the end of the World War II relations between the two states rapidly improved but this development was abruptly interrupted by the escalation of the Soviet–Yugoslav conflict following the 1948 Tito-Stalin split.^[6] Tensions eased in 1953 after Stalin's death.^[6]