American involvement in Vietnam began in the mid-1950s, as the French, defeated on the battlefield by the communist Viet Minh, began to withdraw all military forces out of their former colony. Fearing a vacuum that the communists might soon fill, the United States helped establish the Republic of Vietnam in the southern half of the country. In the face of North Vietnam's determination to unite all of Vietnam under its control, a series of U.S. administrations provided support to the South Vietnamese government—first with economic and military aid under President Dwight D. Eisenhower, then military advisors under President John F. Kennedy, then combat troops under President Lyndon Johnson, and finally by invading Cambodia under President Richard Nixon.

As the commitment to Vietnam grew, so did protest at home. Many Americans (often, but not always, college students) opposed the war on moral grounds, frequently extending their...