One of the best books on the war is This Kind Of War by T.R. Fehrenbach. Originally published in 1964, it was reprinted by Brassy's in 1999. It goes into the background of the entire war including the 50-year Japanese occupation and the 1945 decision to partition based on occupation zones. It goes into the tension and both sides of administration from 1945 to the war starting on June 25th 1950. Basically, both sides wanted to unify Korea and the communists (PRC and USSR) misread US resolve and decided the "allies" would accept a military fiat accompli.
McArthur did want to use nuclear weapons against China to punish them for sending in their "volunteers" after the NKPA was destroyed in the Fall of 1950. This would never have happened of course. McArthur's hard-pressing for this and his virtually direct challange to Truman on who was running the war cost him his job.