World War I was fought between the Allied (Entente) Powers of Great Britain, France, and Russia against the Central Powers of Germany, Austria-Hungary, and the Ottoman Empire. Italy was originally part of the Central Alliance, but switched sides before committing troops, joining the Allied cause in 1915. In 1917, The United States joined the war on the side of the Allied Powers.

FDR’s “cash-and-carry” policy was an amendment to the Neutrality Act. Roosevelt pushed Congress to pass the measure so that the United States could support the allied powers without giving up their claims to neutrality. The “cash-and-carry” policy stated that warring nations could purchase arms from the United States, so long as they paid in cash and carried the weapons away on their own ships. 

Richard Nixon opened relations with Mao’s China when he visited Beijing in 1972. Prior to Nixon’s visit, relations between China and the United States had been extremely negative. The United States recognized the nationalist government of Taiwan as the legitimate government of China. Nixon’s visit, and Kissinger’s diplomacy, reversed this policy. At the time many people believed this to be one of the most important turning points in the Cold War. It did lead, eventually, to a massive growth in trade agreements and social exchange between the two nations and, some historians maintain, helped isolate the Soviet Union and bring about the end of the Cold War.

The Dawes Plan, proposed in 1924, was an attempt to solve the massive economic and diplomatic problems caused by the Treaty of Versailles. The Treaty declared Germany responsible for the outbreak of war and mandated that Germany pay reparations to Great Britain and France. Additionally, Britain and France owed a substantial amount of money to the United States. Germany, due to extreme economic difficulties, was largely unable to pay back the money. The Dawes Plan proposed that United States’ banks would lend money to Germany with a generous payment plan in place. The Germans would then in turn pay reparations to Great Britain and France, and they would pay back their debt to the United States. At the time it was enough to earn Dawes the Nobel Peace Prize; however, as you can imagine with such an obviously circular mechanism, it did not wholly work and was replaced in 1929 with a different plan. 

Brinksmanship refers to an aggressive form of diplomacy that requires pushing dangerous events to the brink of a declaration of war, in order to gain the most advantageous positing for aggressor. The policy, along with the corollary phenomenon called "Mutually Assured Destruction," defined the relationship between the United States and the Soviet Union throughout the Cold War. The term began to be used during the Eisenhower administration and can be observed in numerous political crises of the twentieth century—for example, the Cuban Missile Crisis. 

In his famous “Fourteen Points” statement, issued at the end of World War I, Woodrow Wilson called for a united League of Nations to police global conflict and work towards a peaceful, cooperative world. The League was written into the Treaty of Versailles and established soon after; however, the Treaty of Versailles and the American entrance into the League of Nations failed to pass the United States Senate: without the membership of its primary charter member, the League was doomed to be ineffective. 

The European Recovery Program, colloquially named after U.S. Secretary of State George Marshall as "The Marshall Plan," was introduced in 1948 to support various Western European countries in their effort to rebuild after World War II. The Program gave direct economic and technological aid to any European country wishing to have it. All the Soviet controlled states refused the aid, as it meant US control over their economies. The Marshall Plan had multiple goals, including rebuilding damaged economies, strengthening democracies, improving the industry of Europe, and ultimately preventing the spread of communism.

In the aftermath of America's participation in World War I, many people in the country did not want to continue with Woodrow Wilson's vision of America's international role that got them into the war. The most profound statements were COngresses refusal to enter Wilson's pet project the League of Nations, and in the success of the Republican Party against Wilson's Democrats in Presidential elections. This meant the Foreign Policy lurched strongly towards the stance of isolationism, or trying not to get involved in any foreign conflicts.

In 1990, Mikhail Gorbachev was ousted in a coup by Soviet hardliners, a move which backfired and saw the dissolution of the USSR, because of his support for nuclear arms reduction with American president George H.W. Bush. While in domestic policy, Bush continued with the same programs as his predecessor, Ronald Reagan, but the fall of communism helped give the foreign policy of Bush a new direction.

"Dollar diplomacy" was the prominent foreign policy approach favored by President William Howard Taft (1909-1913), but was widely used before and after Taft's term in office. The general principle of dollar diplomacy was that financial, rather than military, muscle was the most effective way of convincing foreign governments to support American interests.