The political slogan "Workers of the world, unite!" is one of the most famous rallying cries of communism. It is found in The Communist Manifesto (1848), by Karl Marx and Friedrich Engels (German: Proletarier aller Länder vereinigt Euch!, literally "Proletarians of all countries, unite!" but soon popularized in English as “Workers of the world, Unite! You have nothing to lose but your chains”). A variation ("Workers of all lands, unite") is also inscribed on Marx's tombstone.
The International Communist League, described by Engels as 'the first international movement of the working class' which united members of the League of the Just, The Communist Correspondence Committee, English Chartists and German refugees across Europe, was persuaded by Engels to change its motto from the League of the Just's - 'All men are brothers' - to 'Working men of all countries, unite!.' 
The phrase has overlapping meanings. First that workers should unite in unions to better push for their demands such as workplace pay and conditions. Secondly, that workers should see beyond their various craft unions and unite against the capitalist system. And thirdly, that workers of different countries have more in common with each other than workers and employers of the same country, and as such was used by the IWW when opposing World War I in both the USA and Australia.
This slogan was the USSR State motto (Пролетарии всех стран, соединяйтесь!Proletarii vsekh stran, soyedinyaytes’!), appeared in the State Emblem of the Soviet Union, on 1919 Russian SFSR banknotes (in Arabic, Chinese, English, French, German, Italian and Russian), on Soviet coins from 1921 to 1934, and in most Soviet newspapers. Contemporarily, some socialist and communist parties[who?] continue using it. Moreover, it is a common usage in popular culture, often chanted during labor strikes and protests
In the first Swedish language translation of the Communist Manifesto, published in 1848, the translator Pehr Götrek substituted the slogan for Folkets röst, Guds röst! (i.e. "Vox populi, vox Dei", or "The Voice of the People, the Voice of God"). Later translations have, however, included the original slogan.
Amongst Maoist-oriented groups a variation invented by Vladimir Lenin, 'Workers and Oppressed Peoples and Nations of the World, Unite!', is sometimes used. This slogan was the rallying cry of the 2nd Comintern congress in 1920, and denoted the anti-Imperialist and anti-Colonialist agenda of the Comintern.