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Part of the cold war; the North invaded the South.
It was to help South Korea and try to contain communism in North Korea
After WW II, the Truman Doctrine was that the United States would provide political, military and economic assistance to all democratic nations under attack from authoritarian nations (ie USSR, North Korea).
North Korea attacked South Korea.
Truman was a proponent of containing Communism and attempted to stop the spread from North Korea to South Korea.
North Korea
russians
president truman ordered american troops moved from Japan to South Korea.
the invasion of South Korea by North Korea
President Truman had developed the "Containment doctrine" that held that Communism must be contained within the areas it then controlled and that every effort to expand its territory further must be 'actively' resisted by the USA. The doctrine was developed after the USSR's Josef Stalin had installed puppet Communist governments in practically all of the countries in Eastern Europe where it had chased out the armies of Nazi Germany. This Truman Doctrine not only led to its involvement in the Korean War, but later also to US policy towards Cuba and finally, to US involvement in the Vietnam war. Since it was Communist North Korea that started the war by invading South Korea, this was a clear case of Communism trying to expand its territory. Since it furthermore clearly was an unprovoked invasion without any preceding declaration of war, the US had no trouble convincing the UN and its members to also come to the aid of South Korea and troops of several Western countries fought North Korea - and later the Chinese forces sent in to support the Korean army.
truman believed it was the soviet communist powers that was truly behind the invasion of south korea
1950, Truman was president