How did South Korea and North Korea become separate countries in 1948?

Following the surrender of Japan in 1945, the Korean Peninsula was liberated from colonial rule but was temporarily divided along the 38th parallel to facilitate the surrender of Japanese forces—Soviet troops accepted the surrender in the north, while U.S. forces did so in the south.12

What was intended as a temporary administrative arrangement hardened into a permanent division as Cold War tensions intensified and efforts to establish a unified government failed. In 1947, the United States brought the issue to the United Nations, which called for general elections. The Soviet Union barred the UN commission from the north, leading to separate developments:13

• South Korea: Held UN-supervised elections in May 1948 and inaugurated the Republic of Korea on August 15, 1948, under President Syngman Rhee.34
• North Korea: Established the Democratic People’s Republic of Korea on September 9, 1948, under Premier Kim Il-Sung.34

Both regimes claimed to be the sole legitimate authority over the entire peninsula, a conflict that eventually escalated into the Korean War.34