The surrender of Germany on May 8, 1945 marked the end of World War Two in Europe. However, along with the fall of Berlin also came a falling-out between the Soviet Union and the United States. Up until the end of the war, the two countries had formed an uneasy alliance in order to defeat a common enemy: Germany. Without the threat of German aggression acting as an adhesive, the cracks in the foundation of the alliance between the two countries could no longer be held together. The Soviet Union and the United States wanted two fundamentally different post-war worlds. The Soviet Union wanted to be surrounded by "communist-friendly" countries, which the USSR would have a great amount of control over and that would act as a buffer zone in the event of another war. The United States wanted a world of free trade, which would also help the U.S. economy avoid a post-war depression, and to introduce the democratic system of government to newly independent countries. Conflict over plans to reconstruct post-war Eastern Europe further illustrated the different aspects of each country's ideal post-war world. Ultimately, the growing conflict between the two countries resulted in the emergence of "a new form of international conflict - a Cold War, or state of mutual hostility short of direct armed confrontation" (Boyer et al., 789). From post World War Two on through the middle of the 1950s, the United States experienced an increasing fear of communist aggression. As the Cold war progressed, the United States used this fear to help shape its foreign policy to achieve its main goals of containing the Soviet Union and halting the spread of communism.

The conflict between the ideal post-war worlds of the United States and the Soviet Union first came to a head as a result of an uprising in Greece in 1946. Communist forces, helped by the communist country of Yugoslavia, threatened to overthrow the government in Greece. The undersecretary of state for the United States, Dean Acheson, warned of the disastrous implications of a communist victory in Greece. These fears were expressed in the 'Rotten Apple Theory:' If Greece went communist, then like a rotten apple in a barrel of fruit, the communist menace would be spread to Africa, Europe, and the middle East. In response to the fear of spreading communism, President Harry Truman reshaped foreign policy through the Truman Doctrine set forth in March of 1947. Truman stated in the doctrine that it must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressure. He realized that the United States could never realize its post-war objectives unless it helped to ensure freedom for all people throughout the world. The policy set forth by the Truman Doctrine came to be known as containment. This policy required the United States to take a defensive posture. Moscow held the knowledge of when it would make its next move firmly in its hands. The United States on the other hand had to wait for the Soviets take the initiative.

Fear of communist aggression led the United States to not only defensively commit to halting the spread of communism, but to actively commit to fighting it as well. The first instance of this new policy came in the Economic Recovery Plan of 1947, better known as the Marshall Plan. Believing that economic stability would translate into political stability, the Marshall Plan sent billions of dollars in economic aid to reconstruct the economies in Western Europe. By the start of the Korean War in 1950, the plan was well in place. As Truman exercised the policy of containment and sent American troops to fight the "Soviet-directed aggression" in Korea, a new fear began to emerge. The possibility arose that the "Soviet-directed aggression" in Korea was just a distraction meant to pull the attention of the United States to the East and away from Western Europe, leaving it vulnerable for a Soviet invasion. However, the Marshall plan had succeeded in rebuilding the economies of Western European countries, thus strengthening their political structures and preventing them from falling to communist takeovers.

Continual conflict between the ideal post-war world of the United States and the Soviet Union led to a full review of American foreign policy by the National Security Council (NSC). Continuing fears of communist aggression were reflected in a policy statement drawn up by the NSC in 1950. This statement, known as NSC-68, would dictate America's foreign policy for years to come. It viewed conflict between the East and the West as inevitable, and any such conflict threatened not just the United States, but all of civilization as well. To check Soviet Aggression, NSC-68 called for increased aid to foreign nations vulnerable to communist aggression along with an increase in defense spending from 5 to 20 percent of the federal budget. Through increased defense spending, the United States hoped to achieve an unmatched atomic arsenal that it could use as leverage when negotiating with the Soviet Union. Indeed, increased spending on American defense would lead to more powerful atomic bombs, the hydrogen bomb, atomic missiles, and atomic-powered submarines. However, the United States was not alone in its atomic supremacy for very long. By 1949, the Soviet Union had successfully detonated its first atomic bomb. Fear of an atomic attack by the Soviets stirred the United States into producing even more atomic weapons. The more weapons the United States built, the more weapons the Soviet Union would build. Eventually, the arms race had supplied both nations with enough atomic weapons to destroy the world several times over. This new threat of global annihilation gave the people of the United States one more reason to fear communist aggression.

Through the early 1950s, fear of communist aggression continued to ripple throughout the United States. By 1953, the United States found itself facing a new front in the Cold War. A new fear emerged that communism was spreading throughout Central and South America like a "rotten Apple." Communist organizations in Guatemala, Brazil, Bolivia, Chile, Colombia, and other Latin American countries began exerting influence on government and labor through peace assemblies, propaganda, magazines, and books. In response, the United States came up with a new tool for use in foreign policy matters: the Central Intelligence Agency (CIA). "Established in 1947 to coordinate foreign intelligence gathering, the CIA became increasingly involved in secret operations to undermine regimes friendly to communism" (Boyer et al. 819). The United States used this new tool not only in South American countries like Guatemala, but throughout the world as well. "By 1957 half of [the CIA's] personnel and 80% of its budget were devoted to 'covert action'- subverting governments, putting foreign leaders on its payroll, supporting foreign political parties, and subsidizing foreign newspapers and labor unions that hewed to a pro-American line" (Boyer et al. 819).

Following the death of Soviet leader Joseph Stalin in 1953, the United States saw a small window of opportunity to eradicate its fears of communist aggression by trying a new approach to foreign policy: peace. Accordingly, President Eisenhower set forth his 5 Points for Peace. The United States hoped that Eisenhower's plan would turn the tide of the Cold War and bring a true and total peace to the world. Along with his 5 Points, Eisenhower laid down steps that the Soviet Union could take to show that its intentions were indeed peaceful. These steps included an honorable armistice in Korea, a free, equal and united Germany, and an independent Eastern Europe. Eisenhower's 5 Points went over like a ripple in a bathtub rather than a tidal wave. The Soviet Union was not about to change its ideological views, and under the leadership of Malenkov, conflict between the United States and the Soviet Union would continue.

From the middle of the 1950s until the Fall of the USSR in 1990, the United States and the Soviet Union would continue to do battle in an effort to bring each of their respective ideal post-war worlds into reality. The United States would continue to exercise its policies established by the Truman Doctrine, the Marshall Plan, and NSC-68 in Europe and Asia in order to halt the spread of communism. "Covert actions" run by the CIA in countries such as Cuba would occur in order to topple already established communist regimes. Fear of communist aggression would continue to fuel America's foreign policy for years to come.