What makes you think so? What about 蒙古and满?

俯首称臣 to them, and celebrating them, but not to Japan? In fact, Japanese followed a lot more Chinese culture at the point of invasion than those 蒙古人 and 满人 did.

In 东北, so many Chinese 俯首称臣 without firing a shot, when 500K soldiers faced 50K invaders.

Not sure whether you based your 坚信 on history or facts, or you just chose to believe. Remember, believing something is easy, because it doesn't require much thinking and effort to study.