"Workers of the world, unite! You have nothing to lose but your chains!" comes directly from
Karl Marx's
Communist Manifesto of
1848, a year in which revolutionary fervor swept
Europe.
Marx concludes his manifesto with this
call to action, hoping that industrial workers in
Europe (particularly
Germany), who lived and worked in
appalling conditions by any modern standards, would rise up and remove their oppressors.
Although the E2 Communist Manifesto node concludes with "Proletarians of all countries, unite!", the website of the American Communist Party, such as it is, contained a version of the CM ending with the actual title of this node.