The Soviet Union would be the correct answer, the Soviet Union was a union with many Eastern European countries containing Russia, Ukraine, Lithuania, East Germany, and Poland, etc.
During the Cold War, the shaded nations were under control of the Soviet Union.
In 1914 and 1941 Germany had attacked Russia through Poland. In 1945 Stalin thought that sooner or later there could be yet another attack through Poland. To stop this he was determined to control Poland and other East European states.
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