This is really controversial, and I am by no means an expert. I think you should look at the work of Korean War scholars such as Sheila Miyoshi Jager, Bruce Cummings, and William Stueck. All of them have different opinions on the subject influenced by personal politics and the time in which they wrote, but if you read all of them you will be able to form your own opinion. My personal favorite is Sheila Jager, but I'm biased because she was my advisor in college, haha.