On November 24, 1918, the Yugoslav National Council--an organization of South Slavic nationalists led by Ante Trumbic of Croatia--addresses Crown Prince Alexander, son of the ailing King Peter and de facto ruler of Serbia, about its concerns regarding Italian claims on South Slavic territory in the former Austro-Hungarian Empire.
According to the Treaty of London, signed by Italy, Britain and France in April 1915, Italy would enter World War I against Austria-Hungary and, in return, receive from the Allies substantial post-war gains of territory, including a large section of Slovenia and the northern part of the Dalmatian coast. On the heels of the armistice of November 11, 1918, Italy had already made moves to reap the benefits of its participation in the war--a situation which, to Trumbic and his fellow nationalists, was intolerable.
"We cannot recognize any contract, not even that of London, by virtue of which, in violation of the principle of nationalities, we should be obliged to surrender part of our nation to other States," the Yugoslav National Council advised Prince Alexander in its statement of November 24. "In full conscience we express our hope that your Royal Highness, with our whole nation, will endeavor to secure that the final frontiers of our State shall be drawn in conformity with our ethnographic frontiers and with the principles put forward by President [Woodrow] Wilson and the other Entente Powers."
South Slavic nationalist aspirations were formalized just days later, with the creation of the "Kingdom of the Serbs, Croats, and Slovenes," a new state containing 500,000 Hungarians and an equal number of Germans, as well as tens of thousands of Romanians, Albanians, Bulgarians and Italians. Trumbic was made foreign minister of the new government, while Prince Alexander was named regent; he would become king two years later, upon the death of his father.
Before then, however, Trumbic and other representatives of the new state would have to stand up for their rights at the post-war peace conference in Paris in 1919. By then, Britain and France had begun to regret their lavish promises in the Treaty of London, while Italy continued to consider the treaty a binding agreement. For his part, Wilson remained committed to the principle of South Slav nationalism and refused to acknowledge Italy's claims on its territory. In a move that infuriated the Italian delegation and caused them to walk out of the peace conference for over a week, Wilson publicly declared that Italy should be satisfied with receiving control over the Trentino and the Tyrol (on the Austrian border), where the majority of the population was Italian.
In the years after World War I, tensions continued within the new South Slav state, driven by the Serbian-dominated government's denial of autonomy to different ethnic groups, most notably Croats and Slovenes. Disillusioned, Trumbic resigned as foreign minister in 1920 and dedicated himself to the protection of minority rights. In January 1929, with the nation on the brink of civil war, Alexander suspended the constitution, dissolved the parliament and all political parties and took dictatorial control. As part of his effort to impose national unity, he renamed the country Yugoslavia.
In 1934, Alexander was assassinated by extreme right-wing Croatian nationalists during a state visit to Marseilles, France. His son, Peter, managed to maintain unity until 1941, when the German army invaded Serbia and Croatia declared its independence.