What was the gulf of tonkin resolution? a. an authorization to use force in korea b. the declaration that the spread of communism wouldn't be tolerated in asia c. a promise to aid the government of south vietnam d. an authorization for the president to use military forces in vietnam

The answer is D. It provided President Lyndon Johnson to use conventional military force in Vietnam.  Initially the U.S. only wanted to assist the South Vietnamese army against the North but eventually it got more involved in the war. Public opinion in America went against the war and that led to U.S. withdrawal from Vietnam.