In grad school, I often cited William Stueck’s Chapter, “The Korean War,” in The Cambridge History of the Cold War. Stueck explains how Kim Il-Sung was able to get Stalin's approval for the his move against South Korea, and the long term ramifications that Stalin's authorization had in the Communist World. If you are not currently at an educational institution that pays for access to this resource, it may be difficult to get cheaply.

Take a look at "Did Stalin Lure the United States in the Korean War? New Evidence on the Origins of the Korean War" by Donggil Kim and William Stueck on the Wilson Center's website. This will give you two different theories of Stalin's role in the Korean War.