Original: Joseph Stalin wanted to bring all of Germany under Soviet influence, but when the West resisted this idea, he sought to create a united Germany which would be non-aligned (the "Stalin Note"). When the West resisted these efforts, Stalin decided to focus his efforts on the Soviet occupation zone.
Simplified: Originally, Stalin wanted to Sovietize all of Germany, but when the West resisted this idea, he tried to work for a united Germany which would be neutral, but when the West again said no he decided to build a new country out of the Soviet occupation zone.