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Basically the Cold War shaped the entire US foreign policy during the period following WW II and the collapse of the Berlin Wall. It took all kinds of shapes, from the "Brinkmanship" policy of Secretary of State Dulles to the "Evil Empire" speech by President Reagan.
Some causes of the Cold War included:
Attempts by the Soviets and Chinese Communists to influence and take over areas in Asia and Europe.
Containment--the policy of the United States to stop communism from spreading to other areas of the world.
The Truman Doctrine--a policy of supporting anti-communist regimes with military and economic aid. The Doctrine was first used in support of democratic governments in Greece and Turkey.
The Marshall Plan--a massive plan to aid in rebuilding Europe after World War II. Western allied nations, as well as neutral nations, and even the Soviet Union were offered economic assistance. The Soviet Union saw this as a threat to their attempt to gain influence in Europe and Asia.
The division of Germany after the war---The Soviets blockaded West Berlin, which was deep within Communist East Germany. The Soviets thought the blockade would allow them to take over all of Berlin. The US replied with the Berlin Airlift, to supply West Berlin.
The North Atlantic Treaty Organization (NATO) was formed in 1949 by the US, Canada, and nine European nations, the first peacetime military alliance in US History. The NATO nations agreed that an attack on one would be an attack on all. The Soviets replied with the Warsaw Pact, a military alliance of communist nations in Eastern Europe.
September, 1949, the Soviet Union tested its first Atomic Bomb.
The Cold War continued through the decades of the 50s, 60s, 70s, and 80s, until the collapse of the Soviet Union and the fall of the Berlin Wall.