Why did north Korean troops invade south Korea

Before 1945 Korea was controlled by Japan. After the Second World War, USA and the Soviet Union split Korea into two. This cause a divide in the country and another divide in the ideals. USA was preaching capitalism and democracy. The Soviet Union, on the other hand, was looking to spread communism. North Korea invaded South Korea to try to form a stable, united Korea as it was before the end of the Second World War. USA acted decisively to defend the South to stop the threat of communism and to continue their policy of containment. They did not want communism to spread.