China: (Chinese sources): 183,108 dead 383,500 wounded 450,000 hospitalized 25,621 missing (Those who defected or were captured were included in missing) 7,110 captured 14,190 defected (U.S. estimates): 400,000+ dead 486,000 wounded
The conflict escalated into warfare when North Korean military (KPA) forces—supported by the Soviet Union and China—crossed the border and advanced into South Korea on 25 June 1950. The United Nations Security Council authorized the formation of the United Nations Command and the dispatch of forces to Korea to repel what was recognized as a North Korean invasion. Twenty-one countries of the United Nations eventually contributed to the UN force, with the United States providing around 90% of the military personnel.
In these and subsequent battles, Seoul changed hands four times, and the last two years of fighting became a war of attrition, with the front line close to the 38th Parallel. The war in the air, however, was never a stalemate. North Korea was subject to a massive U.S. bombing campaign. Jet fighters confronted each other in air-to-air combat for the first time in history, and Soviet pilots covertly flew in defense of their communist allies.
The fighting ended on 27 July 1953, when the Korean Armistice Agreement was signed. The agreement created the Korean Demilitarized Zone (DMZ) to separate North and South Korea, and allowed the return of prisoners. However, no peace treaty was ever signed, and the two Koreas are technically still at war, engaged in a frozen conflict. In April 2018, the leaders of North and South Korea met at the DMZ and agreed to work towards a treaty to formally end the Korean War.
In the US, the war was initially described by President Harry S. Truman as a "police action" as the United States never formally declared war on its opponents and the operation was conducted under the auspices of the United Nations. It has been sometimes referred to in the English-speaking world as "The Forgotten War" or "The Unknown War" because of the lack of public attention it received both during and after the war, relative to the global scale of World War II, which preceded it, and the subsequent angst of the Vietnam War, which succeeded it.