It started with the Truman Doctrine (1947) that stated the United States would help any country financially and militarily that was interested in keeping the world free for democracy. The Truman Doctrine came about as direct result of communist guerillas in Greece trying to take over the government. American advisers believed that the guerillas were taking orders from the Soviets after they launched a civil war against the government. The United States decided to assist the standing government in Greece because they believed it would have a large impact on Europe and most importantly Turkey that was having its own problems with communism and was strategically located next to large oil reserves of Iran. Congress approved $300 million to aid Greece and $100 million in food and military expenses to aid Turkey.
The second large step in containment was the Marshall Plan. Proposed by Secretary of State George Marshall, it would provide economic relief to rebuilding Western European nations such as Great Britain, France, Belgium and even Germany. By boosting European economies the United States would insure that communism does not rise in any of these countries from a weak economy. It also was in American interest to rebuild European economies to market American goods in Europe and to receive the money Britain and France borrowed during the war. Congress wasn't in favor of the proposed plan at first but following a coup by communist in Czechoslovakia, they approved it.
With the Marshall plan helping to rebuild European industries and cities, Britain and France started to concentrate on reforming the currency of West Berlin. Trying to forestall that development Soviet Union imposed a blockade on all railroads, highways and rivers leading to West Berlin. Without thinking twice president Truman airlifted 2.5 million tons, one ton per person, of food and fuel over the blockade which later persuaded Stalin, the Soviets party leader to take the blockade down.
After the coup of Czechoslovakia, U.S. thought that they were in need of an official alliance with the counties opposing communism. NATO (North Atlantic Treaty Organization) was founded in April 1949. They agreed that they would stand by each other, as one and any attack on a member of the alliance is an attack on all constituents. In 1949 in response to NATO the Soviet Union formed the COMECON (Council for Mutual Economic Assistance) as a result of the Warsaw Pact, in 1955 that included Eastern European nations such as Poland, Romania, Yugoslavia and Soviet Union.
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