Theorien über den Mehrwert
Engels developed what is now known as Marxism together with Karl Marx. In 1845, he published "The Condition of the Working Class in England", based on personal observations and research in English cities. In 1848, Engels co-authored "The Communist Manifesto" with Marx and also authored and co-authored (primarily with Marx) many other works. Later, Engels supported Marx financially, allowing him to do research and write "Das Kapital". After Marx's death, Engels edited the second and third volumes of "Das Kapital". Additionally, Engels organised Marx's notes on the "Theories of Surplus Value" which were later published as the "fourth volume" of "Das Kapital". In 1884, he published "The Origin of the Family, Private Property and the State" on the basis of Marx's ethnographic research.