When the north koreans overran south korea in the summer of 1950 united nations forces stopped there advance at?

When the North Koreans overran South Korea in the summer of 1950, United Nations forces stopped their advance at The Pusan Perimeter.

The Battle of Pusan Perimeter was a large-scale battle between United Nations and North Korean forces lasting from August 4 to September 18, 1950. It was one of the first major engagements of the Korean War.