During his convalescence he read Marx, Engels and Rudolf Hilferding and eventually became a communist, mainly by the influence of the father of a nurse with whom he had developed a relationship. He spent the remainder of the war studying economics at the universities of Kiel, Berlin and Hamburg. In Kiel, he witnessed the sailors' mutiny which helped spark the German Revolution and joined the Independent Social Democratic Party. He subsequently moved on to Berlin, but arrived too late to participate in the Spartacist uprising. Sorge received his doctorate in political science (Dr. rer. pol.) from Hamburg in August 1919. By this time he had joined the Communist Party of Germany (KPD), and was engaged as an activist for the party in Hamburg and subsequently Aachen. His political views got him fired from both a teaching job and coal mining work.