Why did the USSR refuse to give up their occupied lands in the Eastern Europe and in Germany?

The USSR refused to relinquish its occupied territories in Eastern Europe and Germany primarily to establish a buffer zone against potential invasions and to spread communist ideology. The Soviet leadership believed that control over these regions was essential for national security and the consolidation of Soviet influence in post-World War II Europe. Additionally, maintaining control over these areas allowed the USSR to support communist movements and governments, thereby reinforcing its geopolitical power during the Cold War.