Once Seoul was liberated the decision was taken to head North. American troops headed North, the South Koreans captured Pyongyang, and US troops headed for the Chinese border.
Once Seoul was liberated, the natural question was: what next? Should the United States cross the 38th parallel and pursue the North Koreans? MacArthur considered it his job to destroy the North Korean Army. Furthermore, he wished to unite the country under President Rhee. MacArthur received authorization to cross the parallel. He was told however, to avoid sending US troops close to the Manchurian or Soviet borders. The fear was always that the Chinese or the Soviets would intervene. The Soviets had made clear that they were distancing themselves from the North Korean venture. The Chinese, however, were signaling to all who would listen that they would not allow US troops to advance towards their borders without intervening. MacArthur and his advisors, however, ignored the signs and pressed on.
On October 9, the 8th Army crossed 38th parallel. For one week, the American army fought hard against the enemy. Then, after one week, the North Korean army broke and headed in a headlong retreat north. On October 19, the first units of the South Korean army entered Pyongyang. On October 20, MacArthur gave the orders to proceed as far as the Chinese border.