Best-case scenario is where Chiang takes down the Communists and warlords, then manages to cut corruption in the KMT to something workable. OTL August Storm is a Chinese operation, and America's original plan of a weakened Japan held down by a powerful China comes to pass. Korean War becomes a walkover, and Vietnam War may not even happen. China likely liberalizes come 1970s, and after the fall of the USSR (may happen sooner, with having to outspend NATO and China), China is the definite #2 in the world, with #1 in reach.