They were a communist single-party system, with properly rigged elections, leaders handpicked by Moscow from the finest Moscow communism schools and a watchful oversight from Moscow. Not just the citizens were kept in line with the rest of the communist block by troops from other communist states, that applied to the leadership as well. Prague spring was the czech leader Dubĉek trying to introduce reforms, angering Moscow, who then invaded and put a stop to that reform nonsense...

The GDR was a dictatorship good and proper. They just avoided giving the impression of having a single leader by speaking through the politbureau. And the local dictators were controlled by the ones in Moscow.