At firs the war in Korea went badly, as the North Koreans pushed the combined South Korean and American forces to the tip of the peninsula. However, General MacArthur reversed the war by a brilliant amphibious assault at Inchon behind the North Korean lines. U.N. forces then proceeded to destroy much of the North Korean army, advancing northward almost as far the Chinese border. MacArthur failed to heed China’s warnings that it would resist threats to its security. In November 1950, masses of Chinese troops crossed the border into Korea, overwhelmed U.N. forces in one of the worst defeats in U.S. military history, and drove them out of North Korea.