IOTL by December 1936, Zhang Xueliang and Yang Hucheng were semi-openly colluding with the CPC, with whom they were in talks of creating a de facto independent Northwestern China (minus Xinjiang) under the guise of "resisting Japanese aggression" [1] with Soviet aid. Chiang Kai-shek has gotten wind of it, or at least suspicious of the lethargy displayed by Zhang and Yang's forces when fighting against the Chinese Red Army (which were in really, really, REALLY dire straits) [2], and had thus made plans to relocate their forces to other parts of China, and their positions at the Northwestern Pacification HQ taken over by loyal men. Naturally, the Xi'an Incident (closer to a Mutiny by nature) derailed said plans. The rest, as they say, is history.
So here's a POD: instead of flying to Xi'an in December 1936, CKS stayed at Luoyang and coordinated the final push against the last CPC holdouts in northern Shaanxi; Zhang and Yang were replaced as planned, their forces moved out of the area, and CKS's boys move in and finish the job. The Chinese Red Army and CPC leadership were thus shattered, rendered powerless and politically irrelevant even if they were alive. The Japanese invade around roughly the same time as OTL, and the Chinese retreated as per OTL; but this time, National Revolutionary Army stay-behind forces wage a more effective campaign without being constantly attacked by Communist guerrillas (it was pretty much official CPC policy to spend most of their effort on expanding their power base behind enemy lines, often at the expense of other NRA forces).
No doubt that corruption and incompetence would still play a part in the ROC government, but better performances in the field would definitely help; remember, OTL WWII for China was Veteran Difficulty (compared to the US's Easy, UK's Regular and USSR's Hardened).
[1] That was a really convenient slogan to gather support in 1930s China and do whatever the hell you damn well please;
[2] The Western Expeditionary Force was surrounded on all side by the Ma Cliques in Ningxia and Gansu, and the main army was trapped in northern Shaanxi and experiencing crippling shortage on anything from funds, food, winter clothing to manpower
Marc A