Short answers, pulled from the story.
The Soviet Union established control over a specific middle portion of Germany on the 2nd of August 1945 through the Potsdam Agreement. This document assigned responsibility for that territory to the Soviet Military Administration in Germany, known by its German initials SMAD.
In April 1946, the Social Democratic Party of Germany merged with the Communist Party of Germany under pressure from the SMAD to create the Socialist Unity Party. This forced union later became the governing party of East Germany and held exclusive power over the region's political landscape by late 1946.
The SMAD established ten special camps for detaining Germans using former Nazi concentration camp facilities. These sites operated as detention centers distinct from regular prisons or labor camps elsewhere in the Soviet sphere and remained active until the early 1950s when many were repurposed or closed down entirely.
In 1947, Allied powers dissolved Prussia and divided its historical territory across central Germany among five German states known as Länder: Brandenburg, Mecklenburg, Saxony, Saxony-Anhalt, and Thuringia. This reorganization replaced older administrative structures with newer regional governments aligned to Soviet interests.
In 1952, Joseph Stalin proposed a united Germany that would remain non-aligned during the height of Cold War tensions through a document known as the Stalin Note. The West showed little interest in pursuing such an arrangement despite repeated diplomatic efforts, which helped cement the identity of the Soviet Zone as a separate state for decades.