Russia wanted to control the countries between itself and Germany. Also wanted to assure his protection
from Germany invading them so they started to control Eastern Europe. That is why Winston Churchill said that a Iron Curtain had fallen in Eastern Europe. It meant that Eastern Europe was separated from Western Europe by different ideas of economy and governments. USA wanted to contain communism and created the policy of containment so Russia could keep what they already controlled but were not allowed to spread more.
Also at Stalin command it was created a blockade to see if USA would try to stop them of doing so. USA did not wanted to go to war and instead they flew over the blockade to bring supplies to people in West Berlin. Later on the Western nations signed a treaty to create NATO. nIt agreed that this nations will go to war to defend any country in the treaty that was attacked. But Germany remain divided. Many people tried to escape from East Germany. Then the government build the Berlin Wall.