The correct answer is the Korean War.
The Berlin Airlift happened a bit earlier, in the years 1948-1949. The military alliance NATO was created on April 4, 1949.
The Korean War ( 25 June 1950 - 27 July 1953 ) was a conflict between North Korea ( supported by China and the Soviet Union ), and South Korea ( supported by the United Nations and the United States ). The war started with the North Korea's invasion over the South Korea following some border clashes.
North Korea was a socialistic state as opposed to the capitalistic South Korea. The United States participated in the war because it wanted to stop the spread of communism in that region ( in case of Norths Korea's victory in the war ). The conflict ended with an armistice that lasts till today.