Korean War two years of fighting became a war of attrition, with the front line close to the 38th parallel. The war in the air, however, was never a stalemate. North Korea was subject to a massive bombing campaign. Jet fighters confronted each other in air-to-air combat for the first time in history, and Soviet pilots covertly flew in defense of their communist allies. The fighting ended on 27 July 1953, when an armistice was signed. The agreement created the Korean Demilitarized Zone to separate North and South Korea, and allowed the return of prisoners. However, no peace treaty was ever signed,
Australia in the Korean War border between North Korea and China, and extend their rollback policy into China. Many in the West, including General MacArthur, thought that spreading the war to China would be necessary and that since North Korean troops were being supplied by bases in China, those supply depots should be bombed. However, Truman and the other leaders disagreed, and MacArthur was ordered to be very cautious when approaching the Chinese border. Except on some rare occasions, UN bombers remained out of Manchuria during the war. China warned American leaders through neutral diplomats that it would intervene to protect its national security, however