As mentioned here, in 1952 Stalin proposed a reunification of Germany and free elections there, in exchange for Germany not being part of NATO.
In 1952 West Germany was not part of NATO. That would only happen in 1955. But West Germany was becoming part of the First World by that time, and Adenauer wanted integration with the western bloc. There were several issues with Stalin's proposal:
- It was unclear just how sincere it was. Stalin had made promises to Poland which had been repudiated. Finnland seemed to be working out, however.
- The western bloc insisted that a free and united Germany would have the right to freely choose any alliance or none, or it wouldn't be free.
- Adenauer did not believe that Germany could afford the army to secure independence without allies.
- The western bloc wanted to a future Germany army to be institutionally integrated with the forces of other countries, so it couldn't become a rogue actor like the Reichswehr.
For the obvious reason that the West would want a reunified Germany be part of NATO. In fact, the same demand was made at the break up the USSR and the Warsaw Pact however Poland, Hungary & the Czech Republic joined NATO, then later seven central and eastern european countries - Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia.