The Austro-Hungarian Socialist Unity Party was the governing Marxist–Leninist political party of the Democratic Republic of Austria-Hungary from its formation in 1958 until it was dissolved after ethnic strife in 1968. It was a merger of the Austrian Communist Party, Hungarian Socialist Workers' Party, Austrian Social Democratic Party, and the Hungarian Socialist Party.
The DRAU functioned nominally as a multi-party state and had democratic elections, however the Socialist Unity Party maintained a supermajority for the 10 years that the socialist Austro-Hungarian state existed. The main opposition to the Socialist Unity Party was an alliance of the Austro-Hungarian People's Party, the Freedom Party and the Christian Democratic Party. In the 1960s, the Socialist Unity Party rejected federalizing Austria-Hungary, which would lead to the Austrians and Hungarians becoming more and more polarized as the ethnic differences could not cope with a unitary state, leading to the party's collapse in Autumn of 1968.
The party's dominant figure and effective leader of East Germany, was former Hungarian leader János Kádár. On 16 December 1968, the Socialist Unity Party dissolved back into the Austrian Communist Party (KPO), and the Hungarian Socialist Workers' Party. However, both parties lost control of their respective nations within 3 months of Austria-Hungary's collapse, abandoning Communism. Austria became a capitalist democracy, and Hungary embracing Democratic Socialism. Hungary became a stable country, however, Austria's near-collapse led to their union with Bavaria and the formation of the South German Federation.