The White House had only wanted to roll back communism to the 38th parallel, an artificially set border. I am not sure whether it was entirely due to MacArthur's influence, but the White House finally agreed that the Korean War was an opportunity to force communism out of Korea. .
The White House's major concern was the Soviet Union and China. How would they respond to such an advance? President Truman was determined to avoid a direct conflict with China or the Soviet Union which could potentially lead to a new world war. However the general feeling within the White House was that the time for Moscow's involvement in the conflict had passed and that the Chinese would stay out of the war if they were given adequate assurances that the UN forces would stop at the Yalu River and not attack China. With the reassurance of the White House, on September 27, Truman gave MacArthur permission to pursue the communists into their own territory. However, the White House advised MacArthur to limit the advance of troops to only the reconstituted South Korean divisions then fighting with the Americans. MacArthur ignored that part of his instructions, and sent his troops, including the Americans, headlong into the north toward the Yalu and Tumen rivers. .
The Chinese Communist regime protested the advancement of troops beyond the 38th parallel. Truman sensed an uneasy situation in Korea and flew to Wake Island in mid October and met MacArthur for the first time. The president had requested to meet with MacArthur but the general claimed that he was too busy with the war to come back to the states. Truman took him at his word and flew the lengthy roundtrip distance of 14,404 miles to meet with MacArthur. The meeting went well and MacArthur was able to provide the assurance that Truman was searching for. MacArthur assured Truman that the Chinese wouldn't enter the war, and even if they did, the greatest number of troops they could hope to maintain in Korea was 50,000 to 60,000.