In 1961 the East German government began constructing a barbed wire barrier system with concrete between West Berlin and West Berlin in order to prevent East Germans from seeking evacuation to the west. This Berlin Wall which is nearly 30 years old is not only a symbol of German division but also a symbol of greater conflict between communist and non communist world. When East Germany canceled entry restrictions in November 1989, the wall was no longer an obstacle. The wall was basically dismantled in the year before the German reunification.
The origin of the Cold War is a controversial topic. There have been many reasons for the development of the Cold War between 1945 and 1949. First, there was an ideological conflict between the West and the Soviet Union. The Western side firmly supports capitalism, but the Soviet Union is enthusiastic about communism. For this ideological conflict, the Soviet Union elected to send troops to Eastern Europe shortly after the withdrawal of the Nazis, which exacerbated tension. Traditionalists believe that the Cold War was caused by Soviet attacks. Therefore, what America does is trying to contain the Soviet Union. Behavior by the Soviet Union, which is considered "aggressive", is offset by US actions. Historians since 1991 stated that the Cold War is a consequence of the fear of Western European Soviet power. So to a certain extent, the Soviet policy is the cause of the origin of the Cold War.
If you do not know yet, the Cold War is a period of fierce competition between the United States and the Soviet Union. The Cold War lasted from the end of the Second World War in 1945 until the collapse of the Soviet Union in 1991. The Cold War was not a real war with people, guns, tanks, fighters, but a fierce war. President Reagan of the two superpowers in the world thinks that the United States needs to have strong military power. He thinks he is willing to negotiate with the Soviets (he does), but he wants to negotiate from a strong position. In 1983, Reagan proposed a missile defense system called Strategic Defense Program (SDI). Basically this is a missile defense system, laser and other state-of-the-art technology can offset future missiles. This project relied on technologies that were not yet available, but this project aroused the fear of the Soviet Union and gave the US an advantage in negotiations. The project has never been fully deployed