The Truman Doctrine was announced by President Harry Truman to a joint session of Congress on March 12, 1947. Truman was specifically responding to political unrest in Greece and Turkey, where it appeared highly likely that Communist governments would take power. Truman asserted that the U.S. would financially assist in any way it could to prevent Communism from spreading, but would nit be involved militarily.

The United States was eager to expand its trade markets, and wanted access to Chinese ports. Various European nations and Japan had succeeded in carving out exclusive trading rights to certain key ports in China, which allowed them to block entire regions from US business. The thriving climate of US economic expansionism encouraged policies such as this one, which was proclaimed by Secretary of State John Hay in 1899, in order to open up all “exclusive” ports to American business, and eliminate the granting of favoritism toward certain countries at Chinese ports.

The Open Door policy was rooted in the desire of U.S. businesses to trade with Chinese markets, though it also tapped the deep-seated sympathies of those who opposed imperialism, with the policy pledging to protect China's sovereignty and territorial integrity from partition.

Throughout the 1980s, Nicaragua was involved in a fierce civil war pitting the left-wing Sandinistas against the right-wing Contras. In the mid-1980s, the Reagan administration openly supported and publicly encouraged the Contras as part of their general anti-communist foreign policy. It was revealed in 1987, however, that the Reagan administration had been giving arms to the Contras that were acquired through secret hostage negotiations with the government of Iran, which had a putative embargo during the period.

The Domino Theory was an integral part of United States anti-Communist policy in the decades following World War Two. Many American politicians maintained that if Communism was allowed to spread it would have a domino effect which would cause other countries to adopt Communism also. It was provided as justification for numerous anti-Communist wars, campaigns and embargos - most notably, throughout Central America and South-East Asia. 

The Paris Peace Accords ended America’s direct involvement in the Vietnam War in 1973. The peace process provided for a ceasefire between North and South Vietnam and the removal of all American military personnel from Vietnamese territory. It was the work of several years of diplomatic maneuvering by Henry Kissinger, United States National Security Advisor, and his Vietnamese counterpart. The Paris Peace Accords were signed during the Presidency of Richard Nixon.

The small conflicts that were “hot” during the Cold War took place over the entire globe, and generally pitted allies of the United States against allies of the Soviet Union.  An “Iron Curtain” existed in Europe from the partition of Germany, down through Czechoslovakia and Yugoslavia, east through the Soviet Union itself.  In other conflicts, including Korea and Cuba, the United States and Soviet Union picked sides in Civil Wars, with the Korean War being fought between Soviet backed North Korea and U.S. backed South Korea.

In the early morning hours of December 7, 1941, Japanese planes appeared over Hawaii and began bombing Pearl Harbor Naval Base.  The next day, President Roosevelt gave a speech declaring war on the Axis powers and made his famous statement about the Japanese attack.

The idea of peaceful diplomatic negotiation coupled with the implied threat of militaristic intervention summarizes the foreign policy beliefs of Theodore Roosevelt during his time as President. It is generally referred to as Big Stick Diplomacy or Big Stick Policy. It was ultimately reversed by Theodore Roosevelt’s cousin, Franklin D. Roosevelt, when he instituted the Good Neighbor Policy – which stated that the United States would no longer interfere in the affairs of its Latin American Neighboring countries. 

The Reagan Doctrine explicitly stated that the USSR was “the concentration of all modern evil” and that the United States had a duty to curb the spread of Communism and support Anti-Soviet movements throughout the world. Although Reagan would have argued in favor of “trickle-down economics” – the policy that tax cuts on the rich will lead to a trickle-down effect whereby the poor are paid more – this idea is better summarized by the term “Reaganomics.” Likewise, Reagan would have also argued that increased military spending was the surest way to protect American interests; however this idea is not covered by the Reagan Doctrine. 

In 1915, US troops invaded Mexico looking for Pancho Villa.  It was also revealed that Germany had tried to form an alliance with Mexico against America, leading to increased tension. Even though Mexico turned down this alliance, relations were strained with the US after the fact.