The dissolution of Austria-Hungary was a major geopolitical event that occurred as a result of the growth of internal social contradictions and the separation of different parts of Austria-Hungary. The reason for the collapse of the state was World War I, the 1918 crop failure and the economic crisis. The 1917 October Revolution and the Wilsonian peace pronouncements from January 1918 onward encouraged socialism on the one hand, and nationalism on the other, or alternatively a combination of both tendencies, among all peoples of the Habsburg monarchy.
The remaining territories inhabited by divided peoples fell into the composition of existing or newly formed states. Legally, the collapse of the empire was formalized in the Treaty of Saint-Germain-en-Laye with Austria, which also acted as a peace treaty after the First World War, and in the Treaty of Trianon with Hungary.