Nobody ever stepped foot on Aboriginal Australian soil either prior to the arrival of the British. That doesn't make the Aboriginals amazing warriors. It just makes them a bunch of losers that hid on an island.
At the height of the Mongol Empire's power (Yuan Dynasty) they had 40 tumen (400,000 Mongol cavalry) under their control. This was the greatest land-based fighting force the world had ever seen at the time. The Mongols already subjugated the entire Asian continent with far less forces. But with the wealth and resources of China under their control, Mongol power arguably reached its pinnacle under the Yuan Dynasty.
After Ming forces got through with the Mongols, only 6 tumen managed to retreat to the steppe. They lost 34 tumen to the Ming. This was the same fighting force that conquered all of Asia, utterly destroyed by the Chinese.
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The Ming Dynasty Yongle Emperor
personally led five military campaigns to kill Mongols LOL.
Yongle Emperor's campaigns against the Mongols - Wikipedia, the free encyclopedia
China has fought wars and faced hardship that Japan could only dream of while squatting on your tiny islands. But it is this very evolutionary pressure that has allowed China to remain on top for thousands of years.
Japan has never fought any real wars.
The 'China' that Japan fought during WWII was a shadow of its former self. It would be like me waiting for Muhammad Ali to develop Parkinson's and then beating him up with a baseball bat.