The Korean War was a war that was fought between United Nations forces and those of North Korea (at first) and then North Korea and China. the United Nations forces were mostly American and were led by American generals.
The war started in 1950 when North Korea invaded South Korea. North Korea almost took all of South Korea in their first push. Then UN forces counterattacked and almost took all of North Korea. At that point the Chinese entered the war.
The war ended in 1953 with just about no change in the borders of North and South Korea.
Korean War refers primarily to war between North Korea and south Korea that began on June 25, 1950 and ended on July 27, 1953. This is the first war in which United Nations Played a Military Role. On behalf of UN 16 countries sent their troops to fight on in this war in support of South Korea, and 41 countries sent military equipment, food and other supplies.
However, USSR supported North Korea by supplying them military equipment. China fought this war on the side of North Korea.
The primary causes of the Korean war was the division of Korea in North and South, after World War II. The North Korea was occupied and controlled by USSR while South Korea was controlled by USA. This division of the country came in way of forming a unified government for the whole country. Instead separate governments in each part were formed that claimed control over the entire country. This resulted in war between the two side.
The Korean war ended with the signing of an armistice between the two sides. However till date there is no permanent peace agreement between them.