In the aftermath of World War II, Germany was divided into four different zones that were occupied by different nations: the United States, the United Kingdom, France, and the Soviet Union. The capital of Berlin was completely within Soviet territory, but it was also similarly divided into four sectors. Over time, tensions between the Soviets and Allied powers developed, both politically and ideologically.
One of the first major international crises of the Cold War was the Berlin Blockade, which lasted from June 1948 to May 1949. During this time, the Soviet Union blocked access to the sectors of Berlin, so the Western allies were unable to use railways, roads, or canals to access Berlin, even though Berlin was also under Western control. As a result of this blockade, the Western Allies organized a way to carry supplies to the people of Berlin through the air, where the Soviets were too afraid of repercussions to attack.
Over the next couple years, more and more people fled from Soviet-occupied East Germany westward. In an attempt to stop the citizens from leaving, the Communist government built a concrete barrier known as the Berlin Wall and said its intended purpose was to keep capitalism out of the communist part of the country. The Berlin Wall was erected in 1961 and was ordered to be torn down in 1989. It included guard towers, anti-vehicle trenches, and other methods of defense.