How did Croatia become part of the Kingdom of Serbs, Croats, and Slovenes in 1918?

Following the collapse of Austria-Hungary during World War I, Croatia sought to avoid being partitioned by the Allies under the terms of the 1915 Treaty of London.1

To secure their future, South Slav leaders in exile formed the Yugoslav Committee, which signed the Corfu Declaration in 1917 with the Serbian government, proposing a unified, democratic monarchy under the Karadjordjević dynasty. Within Croatia, the Sabor voted in October 1918 to sever ties with the Habsburgs and transferred power to the National Council of Slovenes, Croats, and Serbs in Zagreb.1

Despite opposition from Stjepan Radić regarding the lack of guarantees for national equality, the National Council moved toward unification. On December 1, 1918, delegates of the National Council met with Serbia’s regent, Alexander I, to formally affiliate with the Kingdom of Serbs, Croats, and Slovenes.12