The Communist International (Comintern), also known as the Third International, was an international organization founded in 1919 that advocated world communism, and which was led and controlled by the Communist Party of the Soviet Union. The Comintern resolved at its Second Congress in 1920 to "struggle by all available means, including armed force, for the overthrow of the international bourgeoisie and the creation of an international soviet republic as a transition stage to the complete abolition of the state". The Comintern was preceded by the dissolution of the Second International in 1916. Vladmir Lenin and Leon Trotsky were both honorary presidents of the Communist International.

The history of socialism has its origins in the Age of Enlightenment and the 1789 French Revolution along with the changes that it brought, although it has precedents in earlier movements and ideas. The Communist Manifesto was written by Karl Marx and Friedrich Engels in 1847-48 just before the Revolutions of 1848 swept Europe, expressing what they termed scientific socialism. In the last third of the 19th century parties dedicated to Democratic socialism arose in Europe, drawing mainly from Marxism. The Australian Labor Party was the world's first elected socialist party when it formed government in the Colony of Queensland for a week in 1899.