· The influence of George Marshall. Although he was no longer the vigorous figure of World War II, Marshall was still revered by Truman, who had unreserved faith in his judgment. Marshall was not a zealous advocate of invading North Korea, but he shared MacArthur's belief that North Korea must be invaded.
· An unwillingness to engage in negotiations with P'yŏngyang, Peking, or Moscow, aimed at gaining a peaceful settlement of the war and unification of Korea. Negotiations with Communists smacked of appeasement and timidity. Furthermore, no senior members of the Truman administration believed that negotiations could result in a satisfactory outcome.
· A new Washington impulse, seldom (if ever) publicly expressed, to assume a power position worldwide and roll back communism. Acheson had planted the seeds of this new concept in NSC-68. Although NSC-68 had not yet been formally "implemented" by the government, as a result of Korea Washington was then embarked on the massive rearmament program recommended in NSC-68. America had intervened in Korea at first merely to "draw a line" on Soviet expansionism, the ultimate expression of the containment policy. The decision to cross the 38th Parallel into North Korea and engage in a "rollback" reflected the new aggressiveness recommended in NSC-68.[12-1]
The pros and cons of crossing the 38th Parallel, and recommended courses of action, were summed up by the National Security Council in a paper numbered NSC-81, produced on September 1. While this paper was a master-piece of equivocation, the thrust was clear. Provided there was no indication of Soviet or Red Chinese intervention, America should persuade the United Nations to pass a resolution authorizing MacArthur's forces to cross the 38th Parallel to destroy the NKPA and to provide for the unification of Korea by free elections.