The US was already involved, long before he took office. The question should read: ...justify America involving US conventional troops and open warfare against North Vietnam?" LBJ justified it by the Tonkin Gulf Incident (sea battles). It was two incidents but considered only one. The TWO naval battles involved the destroyers USS Maddox & USS Turner Joy against the North Vietnamese Navy Torpedo Squadron 135 on 02 & 04 August 1964.
Prior to this, the US was NOT WAGING WAR against North Vietnam; it was fighting a counter-insurgency war only against local communist guerrillas in South Vietnam. Those local guerrillas were called the Viet Cong (VC).
After the Gulf incident, the US was at war with North Vietnam DIRECTLY. US conventional troops landed in SOUTH Vietnam in 1965.
The Tonkin Gulf incident
Opposition to the Vietnam war caused President Lyndon Johnson to halt aerial bombing of the North Vietnamese and engage in peace talks instead of escalating the war.
Nixon liked football, he played to win. Johnson wanted to create a "Great Society" of peace, education and equal rights. Johnson "Hated" the Vietnam War. He refused to remain president anymore because of it. Nixon was ready to play "hard-ball", and he did.
Johnson
Lyndon B Johnson
The US had military advisers in Vietnam under Kennedy, but the was did not really start for the US Johnson became President.
Opposition to the Vietnam war caused President Lyndon Johnson to halt aerial bombing of the North Vietnamese and engage in peace talks instead of escalating the war.
By escalating it.
Johnson and Nixon
Johnson.
Johnson and Nixon.
Nixon liked football, he played to win. Johnson wanted to create a "Great Society" of peace, education and equal rights. Johnson "Hated" the Vietnam War. He refused to remain president anymore because of it. Nixon was ready to play "hard-ball", and he did.
The Gulf of Tonkin Resolution gave President Lyndon B. Johnson the authority to aid any Southeast Asian country being threatened by communist aggression. He used this as justification for open warfare against North Vietnam.
I believe that was Lyndon B. Johnson. America's involvement in Vietnam was limited until he became president. According to Wikipedia, "It was Johnson who began America's direct involvement in the ground war in Vietnam." See the Related Links below for more information.
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Johnson
He stopped the bombing of North Vietnam.
There is no question that President Lyndon Johnson was in charge of America's military effort in Vietnam, as Commander In Chief, and the war escalated because he escalated it.