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,
Soviet Union in the Korean War the United States and its allies elsewhere, which could have led to a nuclear war. By officially denying its participation, the Soviets prevented the Korean War from escalating. Participation on the North Korean side was also contrary to the UN Security Council Resolution 84 by which the Soviet Union was technically bound. Along with several "Eastern Block" countries (notably Czechoslovakia), the Soviet Union sent over 20 doctors to Korea to aid Communist forces there, similar to Indian, Italian, Norwegian, Danish and Swedish medical detachments in Southern Korea who did not have military force engaged, but merely offered humanitarian support instead.