At its core a civil war, the Korean War pitted South Korea (Republic of Korea) against North Korea (Democratic People's Republic of Korea) in a struggle to reunite a nation divided in the aftermath of World War II. Fighting alongside the Republic of Korea Army were American and other forces mobilized under the banner of the United Nations (UN). The (North) Korean People's Army was joined by Chinese army forces and supported by the Soviet Union.
The underlying cause of the Korean War was the nature of the post–World War II occupation of Korea. Since 1910 Korea had been controlled by Japan and then Allied troops occupied the former Axis possession following