<P> After the first two months of war, South Korean and U.S. forces rapidly dispatched to Korea were on the point of defeat, forced back to a small area in the south known as the Pusan Perimeter . In September 1950, an amphibious UN counter-offensive was launched at Incheon, and cut off many North Korean troops . Those who escaped envelopment and capture were forced back north . UN forces rapidly approached the Yalu River--the border with China--but in October 1950, mass Chinese forces crossed the Yalu and entered the war . The surprise Chinese intervention triggered a retreat of UN forces which continued until mid-1951 . </P> <P> After these reversals of fortune, which saw Seoul change hands four times, the last 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 . </P> <P> 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 has been signed, and according to some sources the two Koreas are technically still at war . </P> <P> As a war undeclared by all participants, the conflict helped bring the term "police action" into common use . It also led to the permanent alteration of the balance of power within the United Nations, where Resolution 377--passed in 1950 to allow a bypassing of the Security Council if that body could not reach an agreement--led to the General Assembly displacing the Security Council as the primary organ of the UN . </P>

Who won the war between north korea and south korea