This is just a map visionalised by KMT but in reality, do Chiang KMT really control that large part of China?Are you so sure? China under the KMT was larger than it is now:
Chiang is the one who signed the treaty to let soviet take over dalian port area for 40years of loan. Chiang is also ready to let tibet goes independent to please the western power.
Chiang is anti communist but he know he has no strength to fight soviet and most likely Outer Mongolia and xinjiang will remain under soviet control. Chiang is a person who believe territories sacrifice to archieve at stabilities and he is very eager to support the west.