President Kennedy was assassinated on 22 November 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. Some have argued that the policy of North Vietnam was not to topple other non-communist governments in South East Asia.