Isolationism or non-interventionism was a tradition in America's foreign policy for its first two centuries.
The League of Nations was created as an international organization after WWI.
Although isolationists kept the U.S. out of WWII for years, the interventionists eventually had their way and the U.S. declared war in 1941.
After WWII, the US's foreign policy was characterized by interventionism, which meant the US was directly involved in other states' affairs.
Truman's Containment policy was the first major policy during the Cold War and used numerous strategies to prevent the spread of communism abroad.
Détente was a period in U.S./Soviet relations in which tension between the two superpowers was eased.
The post-Cold War era saw optimism, and the balance of power shifted solely to the United States.
The War on Terror refers to an international military campaign begun by the U.S. and the U.K. after the 9/11 terrorist attacks.