A saying from later generations put it well: history was the foundation of a nation, and heroes were the bedrock of a nation. A nation without history was ultimately rootless duckweed; a nation without heroes could never truly stand tall!
That was true for a nation, and even more so for a race!
By the later ages, Humanity had become a scattered mess. Human nations stood side by side, each governing itself, waging war against one another, with not even a shred of racial pride remaining.
Everyone stood from the perspective of their own nation. Few could stand from the perspective of Humanity as a whole. Why?
At its root, their cohesion was insufficient. The humans of each nation did not identify strongly enough with their race.
Humanity was scattered throughout the entire Primordial World and could not effectively unite.
The main reason was that during the Investiture of the Gods, the Son of Heaven replaced the Human Emperor. Humanity lost its own Humanity's Co-Lord, and the entire race split apart, never again united as one.
Besides that, another reason was that Humanity lacked its own history. The deeds of Humanity had not all been passed down, leaving only scattered fragments recorded and circulated among humans as mythological tales.
When later Humanity began recording history on a large scale, it was already after the Zhou Dynasty. By then, the Human Emperor no longer existed. Standing upon the vast lands of the Primordial World were only individual human nations.
Thus, later Humanity displayed a phenomenon: they possessed a stronger sense of belonging toward their nations, while their sense of belonging toward their race was not particularly strong. This was also a minor reason why later Humanity became so divided.
Though it was not the primary reason, it was still a reason