Final answer:
The invasion of South Korea by the North was halted by the United Nations forces, mainly led by the United States, following the successful Inchon Landing. The conflict was finally paused with the Korean Armistice Agreement in 1953, leading to the establishment of the Korean Demilitarized Zone.
Step-by-step explanation:
The invasion of South Korea by North Korean forces was curtailed by a significant police action involving United Nations forces, spearheaded by the United States. This intervention began after North Korea's invasion in June 1950, which resulted in the capture of Seoul and a retreat by South Korean forces.
The turning point came with the Inchon Landing on September 15, 1950, a strategic and surprise amphibious assault led by U.S. General Douglas MacArthur, which successfully pushed back North Korean troops and led to the recapture of Seoul.
The war continued with back-and-forth advances until a ceasefire was established with the signing of the Korean Armistice Agreement on July 27, 1953. This agreement created a demilitarized zone near the 38th parallel, the line that still divides North and South Korea today.
The armistice halted outright hostilities and established conditions that prevent the resumption of fighting, while U.S. troops have remained in South Korea ever since as a deterrent to any future aggression.