World revolution is the Marxist concept of overthrowing capitalism in all countries through the conscious revolutionary action of the organised working class. These revolutions would not necessarily occur simultaneously, but where local conditions allowed a revolutionary party to successfully replace bourgeois ownership and rule, and install a workers' state based on social ownership of the means of production.
The end goal is to achieve world socialism, and later, stateless communism.
Arguably, the international situation in the years immediately following World War I was the closest the world ever came to such a revolution. The October Revolution of 1917 in Russia sparked a revolutionary wave of socialist and communist uprisings across Europe, most notably the German Revolution, the Hungarian Revolution, Biennio Rosso and the revolutionary war in Finland with the short lived Finnish Socialist Workers' Republic, which made large gains and met with considerable success in the early stages; see also Revolutions of 1917-23.
Particularly in the years 1918-1919, it seemed plausible that capitalism would soon be swept from the European continent forever. Given the fact that European powers controlled the majority of Earth's land surface at the time, such an event could have meant the end of capitalism not just in Europe, but everywhere. Additionally, the Comintern, founded in March 1919, began as an independent international organization of communists from various countries around the world that evolved after the Russian Civil War into an essentially Soviet-sponsored agency responsible for coordinating the revolutionary overthrow of capitalism worldwide.
After those events and up until the present day, the international situation never came quite so close to a world revolution again. As fascism grew in Europe in the 1930s, instead of immediate revolution, the Comintern opted for a Popular Front with liberal capitalists against fascism; then, at the height of World War II in 1943, the Comintern was disbanded on the request of the Soviet Union's Western allies.
Post World War Two
Revolts across the world in the 1960s and 1970s, coupled with the Chinese Cultural Revolution, the establishment of the New Left together with the Civil Rights Movement, the militancy of the Black Panther Party and similar armed/insurrectionary "Liberation Front" groups around the globe, and even a bit of a resurgence in the labor movement for a time once again made it seem as though world revolution was not only possible, but actually imminent; thus, there was a common expression, "The East is Red, and the West is Ready". However, this radical left spirit soon ebbed in the 1980s and 1990s in face of a right-wing, conservative backlash (spearheaded, among other examples, by Thatcherism in the United Kingdom and Reaganomics in the United States) and also free-market reforms in China and in Vietnam.
Within Marxist theory, Lenin's concept of the labor aristocracy and his description of imperialism, and – separately, but not necessarily unrelatedly – Trotsky's theories regarding the deformed workers' state, offer several explanations as to why the world revolution has not occurred to the present day. Many groups, however, such as the Progressive Labor Party (United States), still explicitly pursue the goal of worldwide communist revolution, calling it the truest expression of proletarian internationalism.