Your discussion of this question should begin with World War II and the German invasion of the Soviet Union.  When this happened, the USSR became one of the Allies.  Because the USSR was one of the Allies, it participated in the setting up of the world after the end of the war.  This process helped to bring the Cold War about.

As the world was being set up, the USSR and the Western Allies divided Europe and, with it, Germany.  The division of Germany made it a focal point in the origins of the Cold War.  This was especially true of Berlin, which was itself divided while being located in the middle of communist East Germany.  The division of Germany and the issue of what to do about the country/countries helped to bring about the Cold War conflict between the superpowers.