Which international conflict did the United States participate in from 1955 to 1975?

The Vietnam War is the correct answer because it was a significant conflict in which the United States was actively involved from the mid-1950s until 1975. The U.S. initially began its involvement as a means to support South Vietnam against the communist North Vietnam, as part of the broader context of the Cold War and the policy of containment aimed at stopping the spread of communism.

During this period, U.S. military personnel and resources were escalated, particularly after incidents such as the Gulf of Tonkin Resolution in 1964, which expanded American involvement. The conflict was characterized by its guerilla warfare, the use of advanced military technology, and significant anti-war sentiment within the United States. The war ended with the fall of Saigon in 1975, marking a pivotal moment in U.S. and Vietnamese history.

The other options do not fit the specified timeline. World War II occurred from 1939 to 1945, which is well before the dates in question. The Korean War, while it did involve U.S. forces, took place primarily from 1950 to 1953, ending before the Vietnam War escalated. The Gulf War started much later, in 1990, and extended into 1991