Background on the Relationship between MacArthur and Truman.
Truman and MacArthur's conflicts arose from the disagreement between the two men. After proposing and executing many well planned plans approved by Truman, General MacArthur sent an ultimatum to China receiving permission from Truman. Truman wished to fire MacArthur, but eventually when he actually got to firing him it was too late because the ultimatum had already ended. Truman then just began to look for reasons to fire the experienced General. Eventually Truman fired him on grounds of insubordination when he MacArthur kept on urging to start directly fighting China and using atomic weapons against the Chinese.