After world war 2 stalin said that soviet union needed a buffer zone to protect it from attack this idea resulted in

The Soviet Union's influence expanded into Eastern Europe.

Context/explanation:

US president Franklin Roosevelt, British prime minister Winston Churchill, and Soviet premier Joseph Stalin, the leaders of the Allies in World War II, met at Yalta in February, 1945.  

Churchill and Roosevelt pushed strongly for Stalin to allow free elections to take place in the nations of Europe after the war. At that time Stalin agreed, but there was a strong feeling by the other leaders that he might renege on that promise. The Soviets never did allow those free elections to occur. Later, Winston Churchill wrote, ""Our hopeful assumptions were soon to be falsified." Stalin and the Soviets felt they needed the Eastern European nations as satellites to protect their own interests.   A line of countries in Eastern Europe came into line with the USSR and communism.  Churchill later would say an "iron curtain" had fallen between Western and Eastern Europe.

arresting and exicuting citizens