If lowly hillbillies like the manchus can do it 500 years before, why can't the great Imperial Japanese Army with their modern equipment as compared to that of the KMT?
the Manchus were brave enough to risk it all and threw in everything to conquer China. the Japanese were not willing to risk it all to achieve their goal. they deployed their forces to China, slowly and one by one in accordance with the situation until they had 1.2 million troops there and were still unable to defeat the Chinese forces. that Japanese small-time gambler mentality was a key reason why the KMT was able to regroup and reorganize, and they effectively checked the Japanese's advances later. the Japanese's early success was a temporary one and came to a halt.
Li Zongren thought if Japan had thrown in more troops at the onset, they would defeat China.
if there was no Chiang Kai Shek, China certainly would be conquered by Japan then. the Chinese people should be eternally grateful to Generalissimo Chiang, not smearing his legacy with all sorts of lies, misinformation and disinformation. Chiang was a great hero of China.