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 both an unreliable and demanding ally and took greater steps to ensure autarky from the USSR in the years following the War. In 1960, China broke from the Soviet Union in an event known today as the Sino-Soviet Split, creating a rift amongst all communist powers which were expected to pick one side of the divide. The North Korean regime, which bordered both countries, successfully navigated the split by playing one power off against the other. It did not firmly align with either power until the Soviet reforms under Mikhail Gorbachev compelled the regime to align with China. This split,