Who is most responsible for the Korean War?

Since Korea has come up in the "Never Forgive Japan" thread, I thought it would be appropriate to have a separate thread for that tangent.

So here is the question I put to the members: Which nation's actions most directly caused the Korean War? Was it America's plan all along to use South Korea to aide the Republic of China (Taiwanese) government against the communists? Did North Korea go off it's leash and start the war to reunify the peninsula on their own terms? Was China seeking expansionism to ensure that they would be too strong to be attacked in the future as they had just been in previous years by Japan?

All I ask is that you support your opinion with reference to historical events and analysis of the motivations behind those actions, and please keep it civil. I think we can have this debate without calling eachother "communist agents" or "imperialists".

My take is a combination. America probably did intend to check Chinese power in the region, and wanted a foothold on the East Asian mainland, but they didn't start the war. The partition of Korea which was caused by the legitimate will of the South not to embrace communism just played into our hands.
Ultimately China and the Soviet Union caused the war by arming North Korea. I believe they sought both to spread communism and in China's case to gain a forward position for any future conflict with Japan, as well as to protect themselves from any percieved possibility that America might undertake a fullscale war with China in defense of the ROC.

I formed my opinion largely based on the information in this wikipedia article, as well as based on some of the reading on Marine Corps History I did in boot camp and shortly afterward.
en.wikipedia.org...