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 precarious relations between both sides, while also offering possible advantages. As American and UN soldiers were already deployed in the war on the South Korean side, it was virtually assured that Soviet forces could not engage in open and direct hostilities against the South without provoking conflicts with other UN countries. Instead, the Soviet Union was compelled to conceal its participation in the conflict (at least to the extent where Soviet involvement could still be plausibly denied by the Soviet government) so as to minimize the risk of escalating the "Cold War" into a "Hot War" with NATO and