The united states involved itself in vietnam in the 1960s because

Communism was spreading and by 1956 the Soviet Union, China, Eastern Europe and North Korea all had communist governments

Explanation:

The war in Vietnam, or the Resistance war against America, as it is known in Vietnam, was a war officially fought between North Vietnam and South Vietnam (from 1955 to 1975). The North was supported by China, the Soviet Union, and other communist allies, while the South was supported, mainly, by the United States and other anti-communist allies. The USA directly and militarily intervened in this armed conflict mainly as an attempt to stop the spread of communism in the region and the world in general. The war itself is considered an important part of the conflicts that fueled the Cold War, which was a historical moment of political tension between the USA and the Soviet Union during the second half of the 20th century.  

answer-the island had airfields that the u.s. military needed.