Escalation refers to the increase or intensification of something, usually in a gradual manner. In the context of American involvement in Vietnam, escalation refers to the progressive increase in military operations and troop deployment.
Related terms
Domino Theory: The belief that if one country falls to communism, neighboring countries will also fall like dominos.
Gulf of Tonkin Resolution: A resolution passed by Congress in 1964 that gave President Lyndon B. Johnson broad authority to escalate military involvement in Vietnam.
Tet Offensive: A major military campaign launched by North Vietnamese forces against South Vietnam and U.S. troops in 1968 during the Vietnam War.