Have you ever tried to corral a bunch of marbles on the floor? They roll around every which way, and just when you think you have them all gathered together, a few more squirt out from your grasp and go skating away. Surely, your job is much easier if you have a few friends to help cage in those marbles.
Though your own travails gathering marbles may seem trivial, the United States' greatest fear in the second half of the 20th century was hemming in a different slippery character: the spread of worldwide communism. For this, the United States gathered its own friends in Western Europe to help stop communism from taking root elsewhere in the world.
After World War II (WWII) ended, the Soviet Union took control of most of Eastern Europe, creating client states in countries such as Poland, Czechoslovakia, and East Germany. The communist Soviet Union and the capitalist West stood toe-to-toe with each other in Germany, especially in the capital, Berlin, where the two worlds were literally separated from each other by the Berlin Wall. The United States feared the spread of Soviet-style, totalitarian communism could threaten Western Europe's capitalist states. Furthermore, if more and more states became communist and integrated into the Soviet Union's command economy, the U.S. could lose important trade and economic partners around the world.
To combat the spread of communism, U.S. foreign policy functioned on the idea of Containment immediately after the war and through the Truman administration. According to the policy, the United States would do everything it could to stop the spread of communism anywhere in the world, be it through diplomacy or military intervention. This policy also inherently intended to avoid open conflict with the Soviet Union, as any military confrontation with the Soviets could possibly lead to World War III.
A complimentary and contemporary theory that helped spur this policy was the Domino Theory. The Domino Theory stated many U.S. government analysts' greatest fears: that if countries in Southeast Asia were allowed to develop communist governments, as China had in 1949, one-by-one the neighboring countries would also become communist, eventually shutting the U.S. out of the region and threatening the U.S. presence.
