Ideologically, the party, from its foundation, adhered to Marxism–Leninism, a fusion of the original ideas of the philosopher and economic theorist Karl Marx, and of Lenin, introduced by Joseph Stalin in 1929, formalized as the party's guiding ideology and remaining so throughout the rest of its existence. The party pursued state socialism, under which all industries in East Germany were nationalized, and a command economy was implemented. The SED made the teaching of Marxism–Leninism and the Russian language compulsory in schools. Walter Ulbricht was the party's dominant figure and effective leader of East Germany from 1950 to 1971. In 1953, an uprising against the Party was met with violent suppression by the Ministry of State Security and the Soviet Army. In 1971, Ulbricht was succeeded by Erich Honecker who presided over a stable period in the development of the GDR until he was forced to step down during the 1989 revolution. The party's last leader, Egon Krenz, was unsuccessful in his attempt to retain the SED's hold on political governance of the GDR and was imprisoned after German reunification.