1. Foundations of Prosperity Created by Natural and Geographic Conditions

The Kumage region, including Iwata, benefited from abundant forests, rivers, and a mild climate, making it highly suitable for permanent settlement from ancient times. This environment ensured stable agricultural productivity and supported a long-lasting sedentary society.
Of particular geopolitical importance was the presence of the “Old Yanai Channel.” Due to marine transgression in antiquity, seawater penetrated far inland, forming calm, channel-like inlets that served as natural harbors. In an era dominated by coastal navigation, these sheltered waterways held exceptional strategic value.
Located at the innermost reaches of these inlets, Kumage functioned as a safe anchorage and logistics hub. By directly linking inland agricultural zones with maritime transport networks, the region established itself as a critical node of distribution, distinct from surrounding areas.

2. Archaeological Evidence of Daily Life and Social Structure

Even before the full centralization of the Yamato state in the early 8th century, the Kumage area already contained a dense concentration of settlements and daily-life remains. Numerous pit dwellings, post holes, ditches, and pits indicate an exceptionally high density of habitation. This contrasts sharply with frontier regions marked by military instability and instead demonstrates the existence of a mature, stable society.
These remains represent a continuous accumulation of human activity dating back to the Yayoi period or earlier. They reveal a long-maintained, production-based sedentary society that endured for centuries.
The spatial continuity of multiple settlements suggests that Kumage was not a single village but a highly integrated regional living and production sphere. This multilayered social structure formed the foundation of the authority that later enabled the construction of large-scale burial mounds.

3. Formation of Regional Clan Power

Supported by stable living conditions and high productivity, Kumage saw the emergence of a managerial elite that oversaw land, water resources, and transportation. Notably, while monumental kofun are relatively limited, everyday life remains are abundant. This suggests that local leaders emphasized administrative and economic control over purely symbolic or military domination.
These clan leaders coordinated agricultural production, mediated inter-settlement relations, and managed maritime traffic along the Old Yanai Channel. Through such practical governance, Kumage had already developed into a semi-autonomous political unit prior to the direct intervention of central authorities.

4. Political Implications of the Name “Kumage”

According to the Sendai Kuji Hongi, during the reign of Emperor Ōjin, a figure named Kame no Omi was appointed as the provincial ruler of Suō. The term “Kuma” (bear / borderland) is significant, as it may have denoted peripheral or formerly non-subjugated groups from the Yamato perspective.
Conversely, the title “Omi” signified a local chieftain who had formally submitted to the central authority. Taken together, the name implies that an originally independent Kumage ruler was incorporated into the Yamato political system and officially recognized as “the Omi of Kumage.”
What name they originally used for themselves, and how they identified their land, remains unknown. Yet the official record invites reflection on the true identity of the “King of Kumage” before incorporation.

5. Subordination and Reorganization under the Yamato State

Archaeological evidence from Kumage shows little sign of abrupt cultural disruption or destruction caused by warfare. This strongly suggests that the region was not conquered through force, but rather incorporated through gradual and cooperative political integration.
Instead of eliminating existing power structures, the Yamato state reorganized local elites as kuninomiyatsuko, regional governors within the imperial system. As a result, Kumage’s leaders retained their local authority while becoming part of the centralized administrative framework.

6. Kumage within the Centralized State

After the establishment of the provincial governance system, Kumage was firmly embedded in the Yamato state through tribute, ritual obligations, and military mobilization. Nevertheless, settlement patterns and daily life show remarkable continuity, with no drastic structural changes.
This continuity indicates that Kumage was not merely a subdued frontier, but a trusted and productive regional base that supported the stability of the ancient state.

7. Summary

The historical trajectory of Kumage can be summarized as: geographic advantage → stable production and settlement → emergence of local clans → submission and reorganization under the Yamato state → continued governance within a centralized system.
This region offers a concrete and highly demonstrative case of how local societies were integrated into the early Japanese state, transforming from an independent polity into a vital administrative and economic center supporting westward expansion.