In the first Korean War these are the countries that sent troops to help South Korea - from http://korea50.army.mil/history/factsheets/allied.shtml :-
Fifteen foreign nations other than the United States and South Korea sent combat forces to serve in the United Nations Command in Korea during the Korean War. Five noncombatant nations provided hospitals or ambulance units. Approximately 150,000 foreign servicemen fought, and foreign casualties included 3,360 killed, 11,886 wounded and 1,801 servicemen missing in action. There were 1,376 foreign prisoners of war repatriated to 12 countries in 1953.
Foreign Ground Forces
Fourteen foreign nations sent ground forces to Korea. Australia, Canada, New Zealand and the United Kingdom comprised the British Commonwealth Forces. Belgium, Luxembourg, Colombia, Ethiopia, France, Greece, the Netherlands, the Philippines and Thailand had battalion-sized units attached to U.S. Army divisions; Turkey deployed an infantry brigade.
Foreign Naval Forces
Eight foreign nations deployed more than 100 naval vessels to Korean waters, including carriers, destroyers, cruisers, frigates, landing ships, tankers and other utility craft. Foreign naval vessels were assigned by U.S. commanders to Task Force 77, the carrier strike force; Task Force 95, the blockading and escort force; Task Force 90, the amphibious landing force; and Task Force 96, the logistical support force.
Foreign naval vessels participated in the Inchon landing; the evacuation of United Nations ground forces from Nampo, Hungnam and Wonsan; shore bombardment of North Korea's coastlines; and patrols of the sea lines of communication to South Korea.
Foreign Air Forces
Australia's 77th Fighter Squadron was the first foreign unit to arrive in Korea on July 2, 1950. It was attached to the 35th U.S. Fighter Group.
South Africa's 2nd Fighter Squadron was attached to the U.S. 18th Fighter Group. It provided close air support to U.N. forces.
Australia, Canada, Greece and Thailand provided air transport units to the United Nations Command.