The Cold War was a period of confrontation and competition between the United States and the Soviet Union. It started at the end of World War II. The United States and the Soviet Union had different economic and political systems. The Soviet Union wanted to spread the Communist system around the world, and we wanted to prevent that from happening.
At the end of World War II, there were several things that led to conflict. In Poland, there were supposed to be free elections to determine the new government. Some members from the prewar government were supposed to be in the new government. The vast majority of people in the new government were members of the government installed by the Soviet Union at the end of World War II. There didn’t appear to be free elections.
The King of Romania said he was pressured to have a communist government. This violated the Declaration of Liberated Europe that was supposed to allow people to choose their own government.
There were also issues in Germany. We believed the Soviet Union was trying to weaken the non-communist zone. As a result, we merged the zones controlled by the United States, Britain, and France into the non-communist country of West Germany. In 1948, the Soviet Union blockaded all land routes into West Berlin. This led to Berlin Blockade.
The Soviet Union tried to spread communism to Greece, Turkey, and North Korea. We opposed the spread of communism because we believed if communism could be contained, the system would eventually fail. Thus, we gave aid to non-communist countries to try to keep them from becoming communist. The Cold War continued until communism basically ended in most places around 1990.