 Engels developed what is now known as Marxist theory together with Karl Marx and 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".