On June 27, 1950, the United States officially entered the Korean War. The U.S. supported the Republic of Korea (commonly called South Korea), in repelling an invasion from the Democratic People's Republic of Korea (commonly called North Korea). The Korean War was a conflict that emerged after World War II. The Empire of Japan had occupied the Korean Peninsula during the war. After Japan’s defeat, the victorious Allies split the peninsula on the 38th parallel. U.S. troops occupied the southern part, while Soviet troops occupied the northern part. The two Koreas engaged in border conflict, which escalated when North Korea invaded South Korea on June 25. The Korean War was a proxy war for the Cold War. The West—the United Kingdom and the U.S., supported by the United Nations—supported South Korea, while communist China and the Soviet Union supported North Korea. The Korean War ended three years later, with millions of casualties. The war ended with virtually no change in the border. The Korean Peninsula is still divided, with military personnel from both North and South Korea occupying the demilitarized zone (DMZ).