Enkyu Ezo War (延久蝦夷合戦)
Enkyu Ezo War was the major warfare occurred in the Heian period. It is also called Eikyu Two-year War or Eikyu War.
It is the war against Ezo/Emishi (the generic name of the native people living in the north part of Japan) by the troops led by MINAMOTO no Yoritoshi, the goovernor of Mutsu Province, and KIYOHARA no Sadahira ("清原貞衡" Studies suggest this Sadahira is the same person with "清原真衡") during the Eikyu era from 1069 to 1074.
The historical process
Emperor Gosanjo carried out a political reformation called Eikyu Shinsei (The New Rule of Eikyu) after the enthronement. Emperor Gosanjo tried to follow the ruling of Emperor Kanmu, and he formulated various policies, to finalize the reconstruction of Imperial Palace, and the subjugation of Ezo (Emishi). Upon the Imperial order of Emperor Gosanjo, the governor of Mutsu Province MINAMOTO no Yoritoshi organized troops in 1070, and left the provincial capital of Mutsu going up to the north.
During the course of this expedition, FUJIWARA no Motomichi (Sani [courtier without post]) seized and ran off with the seal of the provincial official and the key of the provincial storage (the proof of the authenticity of the provincial official status). The governor of Shimotsuke Province, MINAMOTO no Yoshiie, notified the Imperial Court that Motomichi surrendered to him along with the seal and the key of the provincial official. The Imperial Court issued a rescript to summon Yoritoshi on September 14 of the same year. Yoritoshi forwarded a report to the Imperial Court dated on February 4 of the next year, that his troops had achieved a great victory in Ezo.
On June 11 of the same year, the Imperial Court ordered Yoritoshi to refrain from leaving Mutsu Province. Although KIYOHARA no Sadahira was granted a reward to be appointed as Chinjufu Shogun (Commander-in-Chief of the Defence of the North) for the victory, MINAMOTO no Yoritoshi did not receive any reward.
The evaluations regarding the consequence of this war are divided into two.
The first theory is that the expedition of Yoritoshi actually ended as a great success as he insisted, by conquering the regions from Tsugaru Peninsula to Shimokita Peninsula and expanding the ruling of the Imperial Court throughout the Honshu Island. In this theory, the main force of the expedition troops was assumed to be the group led by Kiyohara clan of Dewa Province, therefore the downfall of MINAMOTO no Yoritoshi did not affect the course of this war. As the result of this expedition against Ezo/Emishi operated long after the earlier expeditions promoted by Emperor Kanmu and Emperor Saga, new counties were established in the territorialized area, such as Kuji County (Mutsu Province) and Nukanobe County. After these events, the northern extremity of Japan was pushed further to the region facing to the Tsugaru Straits (which was considered to be the eastern extremity at that time) until the end of Edo period before the modern era of Japan.
The other theory assumes that the expedition was called off because of the downfall of the supreme commander Yoritoshi, therefore the expedition was half-finished. This theory mentioned the awkward point of the expedition troops marching and fighting in the severe winter conditions of the northern part of Japan; it is assumed that the report of Yoritoshi to the Imperial Court stating the grand victory over Ezo was exaggerated in order to cover up his disgraceful matter of losing the important official instruments; in reality, the conquest of Tsugaru and Shimokita Peninsula regions to be ruled under the Imperial Court was succeeded by the later expeditions operated by Kiyohara clan, or even later by the Oshu Fujiwara clan.
As the result of Zenkunen War, (the Twelve-year War of Oshu) Abe clan of Mutsu Province (Oshu, the alternative name of Mutsu Province area) went to extinction, and Kiyohara clan of Dewa Province took control of both Dewa and Mutsu Provinces. At the same time, Toiseibaiken (the right of ruling the north-eastern regions of Japan) split into two authorities as Mutsu Province Chinjufu (the defense capital of the North) and Akita-jo Castle of Dewa Province were integrated into Chinjufu as a single authority.
The main force of the Enkyu Ezo Imperial Court expedition troops was considered to be the troops led by Kiyohara clan. There was a disgraceful matter during this expedition that the official seal of Mutsu Province was stolen. Another theory states that this matter was actually the intrigue of MINAMOTO no Yoshiie plotted against Yoritoshi, sprung from the fear for Yoritoshi to establish his influence in Mutsu Province.
As the result of this expedition, only KIYOHARA no Sadahira was rewarded for the victory by being appointed as the Chinju-fu shogun (Commander-in-Chief of the Defense of the North), which strengthened the presence and influence of Kiyohara clan in Mutsu Province. However, studies also suggest that although Kiyohara clan was boasting the ironclad solidarity during Zenkunen War period, the discord and frustration against the head of the clan Sadahira was developed within the clan after the Enkyu Ezo War, causing the Gosannen War that led the downfall of Kiyohara clan.
The report of Yoritoshi to the Imperial Court mentioned that his troops had reached to 'Ezogawa Keshima,' although the location of this 'Ezogawa Keshima' has not been clarified today whether 'Ezogawa Keshima' was located in Ezo (Hokkaido Island) or the in the northern part of Honshu Island; it is also considered that Yoritoshi exaggerated the military gains and other results in his report. The historical records and the evidence of this war are limited, thus there are many unclear points to be clarified before published in textbooks as a historical fact. Progress in the study regarding this event is expected in the future.