during the korean war what prevented the southern part of the peninsula from falling permanently to the invading forces?

During the Korean War (1950-1953), the southern part of the peninsula, specifically South Korea, was prevented from falling permanently to the invading forces primarily due to the intervention of United Nations (UN) forces, led by the United States.

The conflict began in June 1950 when North Korean forces, supported by the Soviet Union and China, invaded South Korea. The United Nations, with the United States playing a significant role, responded by sending military forces to aid South Korea. General Douglas MacArthur commanded the UN forces.

In September 1950, UN forces conducted a successful amphibious landing at Incheon, which led to a reversal of the North Korean advance. Subsequently, UN forces pushed North Korean forces back across the 38th parallel, aiming to reunify the Korean Peninsula under a non-communist government.

However, as UN forces advanced toward the border with China, Chinese forces intervened in support of North Korea. The conflict escalated into a protracted war with back-and-forth movements along the Korean Peninsula. The 38th parallel, which initially marked the border between North and South Korea, became the de facto boundary, and an armistice was signed in 1953.

The intervention of UN forces, particularly those led by the United States, prevented the permanent occupation of South Korea by the invading North Korean forces and contributed to the establishment of the demilitarized zone (DMZ) that continues to separate North and South Korea today.