The Communist Manifesto — Marx & Engels (1848)

The Communist Manifesto's 23-page call — "Workers of the world, unite!" — became the ideological foundation for communist movements that governed over 1.5 billion people by 1980, or roughly one-third of humanity. Marx and Engels’ analysis of capitalism as a class system driven by exploitation of labour offers a penetrating critical framework that still shapes academic discourse in sociology, economics, and political science. Despite its prescriptive failures, its influence on 20th-century governance outperforms #2's economic impact in sheer demographic reach.