The Socialist Unity Party of Germany (SED) was a Marxist-Leninist communist party that ruled over East Germany from 1949 to 1989.
The SED was founded on 21 April 1946 by a merger of the SPD and KPD in the Soviet occupation zone of Germany and Berlin; the Soviet occupation authorities pressured the SPD's eastern branch to merge with the KPD, and the party struggled with convincing the masses that it was an authentic German political party and not a tool of the Soviet occupation force. The merger was also rejected by many former KPD members, who believed that the KPD would have been more successful alone than in alliance with the untrustworthy Social Democrats. In addition to social democrats and communists, the SED integrated former Nazis into the party; by 1954, 27% of the SED's membership and 32.2% of its public servants were ex-Nazis. The SED's creation of the National-Democratic Party of Germany (NDPD) as an outlet for former Nazis and Wehrmacht officers failed to halt the SED's absorption of former Nazis. During the late 1940s, the SED purged most recalcitrant Social Democrats from tis ranks and became a full-fledged communist party by East Germany's formal establishment in 1949. The party gained a reputation as one of the most hardline parties in the Soviet bloc, holding an orthodox line even amid the glasnost and perestroika era of the 1980s.
On 7 October 1989, the 40th anniversary of the founding of the German Democratic Republic, the old SPD was illegally refounded as the Social Democratic Party in the GDR. The rest of October saw the onset of political turmoil in the GDR as Erich Honecker was deposed by Egon Krenz, whose purported reformism failed to satisfy the public. On 9 November, the SED allowed East Germans to visit West Germany without official permission, resulting in the public demolishing the Berlin Wall. On 1 December 1989, the Volkskammer rescinded the clause in the GDR Constitution that defined the country as a socialist state under SED leadership, and, on 3 December 1989, the entire SED Central Committee and Politburo resigned.
Gregor Gysi took over the SED's leadership and repudiated everything the party had done since 1949. The party pushed out its hardliners like Honecker and Krenz and rebranded itself as the "Party of Democratic Socialism" (PDS) in December 1989. In February 1990, the party abandoned the SED moniker and fully renamed itself to the PDS, and, the next month, it was roundly defeated in the GDR's only free elections. The PDS would be represented in the Bundestag of a united Germany without interruption until 2007, and it merged into Die Linke in 2007.