The Korean War was fought between North Korea, backed by China and the Soviet Union, and South Korea, backed by the United Nations with principal support from the United States. Korea had been divided into two sovereign states in 1948, with North Korea established as a socialist state under communist leadership and South Korea as a capitalist state, while both claimed to be the only legitimate government of all Korea and neither accepted the border as permanent. After a series of border clashes, North Korea invaded South Korea on 25 June 1950, abandoning subversion for open attack. The United States viewed the invasion as communist aggression and sought United Nations help, and the U.N. Security Council met in emergency session as the Soviets walked out. The U.S., the U.N., and sixteen member nations came to South Korea's aid. On June 27, 1950, the United States joined the war. On September 15, the United States and the U.N. led an amphibious invasion of Inchon and regained much of South Korea. After U.S. and U.N. advances north to near the Chinese border in October, China entered the war. Peace talks began on February 1, 1951, after U.S. and U.N. troops retreated to the South, but the fighting continued for two more years. On 27 July 1953, an armistice was signed that created the Korean Demilitarized Zone to separate North and South Korea and allowed the return of prisoners, but no peace treaty was ever signed, so the two Koreas are technically still at war.