High Quality Content by WIKIPEDIA articles! The Battle of Pusan Perimeter was a large-scale battle between United Nations (UN) and North Korean (NK) forces lasting from August 4 – September 18, 1950. It was one of the first major engagements of the Korean War. An army of 140,000 UN troops, having been pushed to the brink of defeat, were rallied to make a final stand against the invading North Korean army, 98,000 men strong.