"The Legality of U.S. Participation in the Defense of Viet-Nam", March 1966

This document, published by the U.S. Department of State, explains why the U.S. government believed its involvement in defending South Vietnam during the 1960s was legal. It argues that under international law and the United Nations Charter, the U.S. and South Vietnam had the right to defend themselves against armed attacks from North Vietnam, including infiltration and military aggression.