Although the United States and the Soviet Union became allies during World War II, there seemed to be little doubt that their opposing ideologies would ultimately produce a cold war. The cold war was a global phenomenon and was clearly conditioned by the political, economic, and social aspirations of the two superpowers. Between 1945 and 1989 Europe became a testing ground for the cold war itself. The Soviets were convinced that Eastern European buffer states had to be created to protect the Soviet Union from future invasions. As for the United States, the Truman Doctrine, Marshall Plan, and NATO were all intended to keep Russian ideology within its own borders. When the cold war came to an end following the collapse of the Berlin Wall in November 1989, the Soviet ideology was considered a spent force in Eastern Europe.