The global shift toward a colder, drier climate brought profound consequences—not only for agricultural societies but for nomadic horse-riding peoples as well.
The horse, as an animal, has a unique digestive system. Its digestive tract is located close to the anus, and it is said that horses expel 70–80% of their food without absorbing its nutrients. This is one reason why horse manure is particularly suitable as fertilizer.
In contrast, cattle are built to absorb nutrients thoroughly. They digest about 70–80% of their intake, excreting very little. Hence, cow manure is far less effective as fertilizer.
This is not a discussion about fertilizer. What's important here is that horses must constantly eat to survive. When cold and dry climates robbed the steppes of their grasslands, horses—unable to store energy—were the first to suffer.
And so, the great migrations of nomadic horse-riders began.
Some of these people eventually made their way to the Wa region (ancient Japan). At the same time, on the Korean Peninsula, deforestation due to iron production caused a severe depletion of natural resources. This, too, spurred migrations in search of forested land. As a result, the native people of Wa were gradually displaced by incoming immigrants.
Thus, both the Yamatai Kingdom and, later, the Yamato court came into being under the leadership of these continental newcomers.
As the Yamato court moved toward a centralized bureaucratic state, its greatest obstacle became the powerful regional clans and tribal leaders who had long held sway over their local domains. Yamatai itself had arisen as a federation of such tribes, and the Yamato polity continued in that tradition. To shift from a federation to centralized rule, the authority of these tribal powers had to be curbed.
As discussed earlier, the gods of these regional clans were, more often than not, ancestral deities. Each tribe believed their own ancestors and their gods to be supreme. To establish a centralized system, the Yamato rulers needed to reorganize and integrate these many gods.
This was the context in which the compilation of fudoki (local gazetteers) was ordered. Based on those submissions, a new mythological structure was constructed—with the Tenson Kōrin myth (the Descent of the Heavenly Grandchild) at its center, and Amaterasu placed at the top of the divine hierarchy. Each clan's status in this new pantheon was determined by its political loyalty and contributions to the emerging state.
It was a centralization of the gods.
Next, atop this newly constructed pyramid of power, emerged Emperor Tenmu—the first ruler to unify religious rites, military command, and political authority in a single sovereign role. He was not a subordinate of the gods, but rather, a god himself. In fact, the divine Amaterasu herself was now placed beneath him in the hierarchy. Thus, the emperor as absolute monarch—a god in his own right—was born.
The once-powerful miko-queen was reduced to a ceremonial figure known as the saiō—a mere ornament of courtly ritual. And those miko who had served at the royal court would soon face a new era, one shaped not by mysticism, but by political design.
（Written by Toshiaki Kiryu）