Outbreak of the Revolt in Gan'gyo (March 15 / 878AD)
More than a half a century of peace came to an end in Gan'gyo 2 (878) as the Emishi of Ideha revolted from Yamato rule. According to Fujiwara no Yasunori Den (Bibliography of Fujiwara no Yasunori), "Akita Castle's governor Yoshimine and his companions did not hesitate to oppress and hoard everything, so that [the people] felt resentment, and anger and thus revolted". This translated into the unfair treatment in trade transactions, and the imposition of heavy taxes on the subject Emishi population.
The war broke out on March 15. In the article found in Nihon Sandai Jitsuroku:
...Governor of Ideha Fujiwara no Ason Okiyo reported through the horse stations, "Emishi rose in rebellion. On [the] 15th of this month, Akita castle, and the district's buildings and houses in the suburbs were burned down. So we are defending ourselves by the peace guards and recruiting an army from the districts."
The following report was sent on March 17 and was received on March 29 in Kyoto. Emperor Yozei was only 11 years old, so the regent Fujiwara no Mototsune sent these orders to both the provinces of Ideha and Michinoku:
To Ideha:
I am aware of the report on the 17th of this month. The Emishi rose in rebellion, attacked and burned the castle and some villages. Dogs or sheep become mad and their nature changes to become violently evil. If we do not subjugate them, what is the punishment? Plan soon to send strong troops and grip [the enemy's] throats. But now in farming season, people are cultivating and sowing. I fear [that] people's work may be hindered if they are mobilized. It is said that the superior strategy in war is to beat [the enemy's] planning, and a good general does not fight. You should pacify the frontier people through skillful strategy. I send the Emperor's other order to Michinoku province. If troop strength in your province is insufficient for suppression, quickly ask Michinoku province for reinforcements. All barbarians change their minds from time to time. Although they are guilty [of rebellion], the policy of the province was not good. You should suspend the creation of conflict through appeasement.
To Michinoku:
I received Ideha province's report on the 17th of this month. The rebels rose, and attacked and burned the castle and villages. The two provinces are adjacent to each other, so [ the author Suzutayu cannot read here. Maybe it says, 'you can know well' ]. If you do not take precautions, you cannot react to emergencies. Increase police efforts to pacify your province. If Ideha province needs reinforcements, send a strong force and help them in a timely manner. In war, swiftness is prized. To not act is shameful. Don't wait until a request has been sent because the opportunity can be lost.