The Kingdom of Yugoslavia was a country in Southeast and Central Europe that existed from 1918 until 1941. From 1918 to 1929, it was officially called the Kingdom of Serbs, Croats, and Slovenes and was colloquially known as Yugoslavia (lit. 'Land of the South Slavs') due to its origins.
The preliminary kingdom was formed in late 1918 by the unification of the Kingdom of Serbia, which was previously independent, with the Kingdom of Montenegro, and the territories of the former Austro-Hungarian Empire, mainly the provisional State of Slovenes, Croats and Serbs (encompassing what is now Bosnia and Herzegovina and most of what are now the states of Croatia and Slovenia) as well as Banat, Bačka and Baranja. The regions of Kosovo and what is today North Macedonia had become parts of Serbia prior to the unification.
The state was ruled by the Serbian dynasty of Karađorđević, which previously ruled the Kingdom of Serbia under Peter I, who became the first king of Yugoslavia, reigning until his death in 1921. He was succeeded by his son Alexander I, who had been regent for his father. In 1929, he established the 6 January Dictatorship, and soon renamed the kingdom Yugoslavia. In 1934, the king was assassinated in Marseille by Vlado Chernozemski, a member of the Internal Macedonian Revolutionary Organization (IMRO), during his visit to France. The crown passed to his 11-year-old son, Peter. Alexander's cousin Paul ruled as Prince regent until 1941, when Peter II came of age following a coup d'etat that reversed Yugoslavia's accession to the Tripartite Pact. The royal family flew to London the same year, prior to the country being invaded by the Axis powers.
In April 1941, the country was occupied and partitioned by the Axis powers. A royal government-in-exile, recognized by the United Kingdom and, later, by all the Allies, was established in London. In 1944, after pressure from the British Prime Minister Winston Churchill, the King recognized the government of Democratic Federal Yugoslavia as the legitimate government. This was established on 2 November following the signing of the Treaty of Vis by Ivan Šubašić (on behalf of the Kingdom) and Josip Broz Tito (on behalf of the Yugoslav Partisans).
Following the assassination of Archduke Franz Ferdinand of Austria by the Bosnian Serb Gavrilo Princip and the outbreak of World War I, Serbia was invaded and occupied by a combined Bulgarian, Austrian and German force on 6 October 1915. This saw the escalation of South Slavic nationalism and calls by Slavic nationalists for the independence and unification of the South Slavic nationalities of Austria-Hungary along with Serbia and Montenegro into a single State of Slovenes, Croats and Serbs.
The Dalmatian Croat politician Ante Trumbić became a prominent South Slavic leader during the war and led the Yugoslav Committee that lobbied the Allies to support the creation of an independent Yugoslavia. Trumbić faced initial hostility from Serbian Prime Minister Nikola Pašić, who preferred an enlarged Serbia over a unified Yugoslav state. However, both Pašić and Trumbić agreed to a compromise, which was delivered at the Corfu Declaration on 20 July 1917 that advocated the creation of a united state of Serbs, Croats, and Slovenes to be led by the Serbian House of Karađorđević.
In 1916, the Yugoslav Committee started negotiations with the Serbian Government in exile, on which they decided on the creation of the Kingdom of Yugoslavia, declaring the joint Corfu Declaration in 1917, the meetings were held at the Municipal Theatre of Corfu.
In November 1918, the National Council of the State of Slovenes, Croats and Serbs appointed 28 members to start negotiation with the representatives of the government of the Kingdom of Serbia and Montenegro on creation of a new Yugoslav state, the delegation negotiated directly with regent Alexander Karađorđević. The negotiations would end, with the delegation of the National Council of the State of Slovenes, Croats and Serbs led by Ante Pavelić reading the address in front of regent Alexander, who represented his father, King Peter I of Serbia (the king of Serbia since the May Coup of 1903), by which acceptance the kingdom was established.
Austria-Hungary collapsed after World War I, and the subsequent Treaty of Trianon in 1920 established the borders of Kingdom of Hungary, and Vojvodina was ceded to Kingdom of Serbs, Croats and Slovenes.
The name of the new Yugoslav state was Kingdom of Serbs, Croats and Slovenes (Serbo-Croatian: Kraljevina Srba, Hrvata i Slovenaca / Краљевина Срба, Хрвата и Словенаца; Slovene: Kraljevina Srbov, Hrvatov in Slovencev) or its abbreviated form Kingdom of SCS (Kraljevina SHS / Краљевина СХС).
The new kingdom was made up of the formerly independent kingdoms of Serbia and Montenegro (Montenegro having been absorbed into Serbia the previous month), and of a substantial amount of territory that was formerly part of Austria-Hungary, the State of Slovenes, Croats and Serbs. The main states which formed the new Kingdom were the State of Slovenes, Croats and Serbs; Vojvodina; and the Kingdom of Serbia with the Kingdom of Montenegro.
The creation of the state was supported by pan-Slavists and Yugoslav nationalists. For the pan-Slavic movement, all of the South Slav (Yugoslav) people had united into a single state. The creation was also supported by the Allies, who sought to break up the Austro-Hungarian Empire.
The newly established Kingdom of Serbs, Croats and Slovenes participated in the Paris Peace Conference with Trumbić as the country's representative. Since the Allies had lured the Italians into the war with a promise of substantial territorial gains in exchange, which cut off a quarter of Slovene ethnic territory from the remaining three-quarters of Slovenes living in the Kingdom of SCS, Trumbić successfully vouched for the inclusion of most Slavs living in the former Austria-Hungary to be included within the borders of the new Kingdom of Serbs, Croats and Slovenes. Nevertheless, with the Treaty of Rapallo a population of half a million South Slavs, mostly Slovenes, were subjected to forced Italianization until the fall of Fascism in Italy. At the time when Benito Mussolini was willing to modify the Rapallo borders in order to annex the independent state of Rijeka to Italy, Pašić's attempts to correct the borders at Postojna and Idrija were effectively undermined by the regent Alexander who preferred "good relations" with Italy.
The Yugoslav kingdom bordered Italy and Austria to the northwest at the Rapallo border, Hungary and Romania to the north, Bulgaria to the east, Greece and Albania to the south, and the Adriatic Sea to the west. Almost immediately, it ran into disputes with most of its neighbours. Slovenia was difficult to determine, since it had been an integral part of Austria for 400 years. The Vojvodina region was disputed with Hungary, Macedonia with Bulgaria, Rijeka with Italy.
A plebiscite was also held in the Province of Carinthia, which opted to remain in Austria. Austrians had formed a majority in this region although numbers reflected that some Slovenes did vote for Carinthia to become part of Austria. The Dalmatian port city of Zadar and a few of the Dalmatian islands were given to Italy. The city of Rijeka was declared to be the Free State of Fiume, but it was soon occupied, and in 1924 annexed, by Italy, which had also been promised the Dalmatian coast during World War I, and Yugoslavia claiming Istria, a part of the former Austrian Littoral which had been annexed to Italy, but which contained a considerable population of Croats and Slovenes.
The formation of the Vidovdan Constitution in 1921 sparked tensions between the different Yugoslav ethnic groups. Trumbić opposed the 1921 constitution and over time grew increasingly hostile towards the Yugoslav government that he saw as being centralized in the favor of Serb hegemony over Yugoslavia.
Three-quarters of the Yugoslav workforce was engaged in agriculture. A few commercial farmers existed, but most were subsistence peasants. Those in the south were especially poor, living in a hilly, infertile region. No large estates existed except in the north, and most of those were owned by non-Slavs. Indeed, one of the first actions undertaken by the new Yugoslav state in 1919 was to break up the estates and dispose of non-Slavic, and in particular Hungarian landowners. Nearly 40% of the rural population was surplus (i.e., excess people not needed to maintain current production levels), and despite a warm climate, Yugoslavia was also relatively dry. Internal communications were poor, damage from World War I had been extensive, and with few exceptions agriculture was devoid of machinery or other modern farming technologies.