Diana posted about other documents from the Cold War International History Project, which reminded me of other resources I've utilized to understand issues like this, specifically, the Foreign Relations of the United States. I was hoping for the volumes on the Korean war, during the Truman administration and the Eisenhower Administration to be online, but as far as I can tell, they are not posted electronically, though I remember one of the pieces we read for yesterday referencing FRUS. I did continue looking, though, and am including those that do have something to do with Korea:
Johnson Administration, including a section about Korea-Japan relations also Japan and China for those interested.
Those are the only ones that, on their face, deal with Korea. (For the China people, there's this one on the opening to China.) Others discuss general economic policy, trade policies, and other things, throughout the different administrations. A complete index of the available FRUS volumes is here.