Communism is a form of government which promotes the idea -- at least in theory -- that the working class should unite and overthrow societal forces which control the means of production and implement common ownership of all resources. Communist thought can be traced to the Renaissance period, but did not take root until the mid-19th century when German communists Karl Marx and Friedrich Engels published their influential "Manifesto of the Communist Party." At its peak in the 1970s and 1980s, roughly one-third of the world's governments were communist. Much of the spread of Communism occurred during Harry S. Truman's presidency.

Communism when Truman Became President

Harry S. Truman was elected Vice President of the United States in 1944 on Franklin D. Roosevelt's Democratic Party presidential ticket. He became president on April 12,1945 when President Roosevelt died in office towards the end of World War II. At that time, the Soviet Union and Mongolia were the only countries with official communist governments, though several Eastern European and Asian countries had significant communist movements vying for power within their countries.

Truman's First Term (1945-1948)

When Truman became president, the U.S. and Britain were allied with the Soviet Union against Germany and Japan in World War II. After the war, the Soviet Union claimed much of Eastern Europe as its "sphere of influence." After the war's end in 1945, communist governments were installed in Poland, Romania, Hungary, Bulgaria and Czechoslovakia. These countries became known as the "Soviet Bloc." Germany and Korea were divided between Soviet spheres of influence -- East Germany and North Korea -- and American and British spheres of influence in West Germany, West Berlin -- which was inside of East Germany -- and South Korea. In 1946, Yugoslavia implemented a communist government modeled after the Soviet Union. The same year, communist forces began fighting the colonial government in French Indochina -- a region that includes Vietnam. In response to growing fear that communism would continue to spread, President Truman outlined a plan to contain the growth of communism in 1947. This became known as the Truman Doctrine.

Truman's Second Term (1949 -1952)

In accordance with the Truman Doctrine, the U.S. gave aid to several governments trying to resist communist movements, including the governments of Greece, Turkey, South Korea, Italy and China. Communist movements failed to gain power in Greece, Turkey and Italy in the late 1940s. However, communists under Mao Zedong gained control of China in 1950. Communist movements led to war in other parts of Asia as well, most notably Korea and French Indochina -- which included Vietnam. The United States fought the spread of communism directly in the Korean War from 1950 to 1953. The U.S. also provided munitions to governments fighting communism in Southeast Asia during the Truman era.

Truman's Influence on Communist Policy

The period between the proclamation of the Truman Doctrine and the collapse of the Soviet Union in 1991 is known as the Cold War. The Truman Doctrine continued to guide U.S. policy throughout the duration of this period. During this time, the United States and the Soviet Union were the two dominant political forces in the world. The two superpowers never fought against one another directly, in large part because both possessed nuclear weapons which they were hesitant to use. Instead, both sides used diplomatic, economic and military means in an attempt to promote their forms of government in less powerful countries.