President Kennedy was assassinated on November 22 , 1963 . Vice President Lyndon B. Johnson had not been heavily involved with policy toward Vietnam ; however , upon becoming president , Johnson immediately focused on the war . On 24 November 1963 , he said , " the battle against communism ... must be joined ... with strength and determination . " Johnson knew he had inherited a rapidly deteriorating situation in South Vietnam , but he adhered to the widely accepted domino theory argument for defending the South : Should they retreat or appease , either action would imperil other nations beyond the conflict
was assassinated
Assassination of John F. Kennedy
Vietnam War