Original: The SED was founded on 21 April 1946 through a merger between members of the Social Democratic Party of Germany (SPD) and the Communist Party of Germany (KPD) who lived in the Soviet occupation zone of Germany and the Soviet-occupied sector of Berlin.
Simplified: The SED was created in 1946 when the Soviet Union forced the Social Democratic Party of Germany (SPD) members and the Communist Party of Germany (KPD) members who lived in the Soviet-occupied parts of Germany and Berlin.