The 'New Emperor' Declaration: Why Did Masakado Style Himself Emperor in 940?

In the first month of 940 (the first month of Tengyō 3), at Iwai in Shimōsa Province (around the modern Bandō City, Ibaraki Prefecture).

Taira no Masakado, who had been attacking the Kantō provincial capitals since the previous November, on this day styled himself 'New Emperor.

' It was an act declaring the establishment of an independent Kantō regime as an emperor in his own right, in place of the Suzaku Emperor of Kyoto.

Masakado was around thirty-eight; only two months from the outbreak of the rebellion to the declaration.

The direct cause of Masakado's subjugation of Kantō was estate strife within the Taira clan.

Killing his uncle Taira no Kunika in 935, internal strife with Taira houses of Kantō expanded thereafter.

In November 939 he attacked the Hitachi provincial capital over conflict with the Hitachi governor, then subdued the Shimotsuke and Kōzuke provincial capitals, bringing nearly all of the eight Kantō provinces under his sphere.

The moment at which the character of the rebellion transformed from local private war to rebellion against the state itself.

'New Emperor' means literally 'a new emperor.' To style oneself a second emperor standing in parallel with the emperor of Kyoto was the first such attempt in Japanese history.

According to the description of the Shōmon-ki, Masakado independently appointed governors of the eight Kantō provinces and aimed at establishing a system of rule completely independent of the Kyoto court.

A challenge to the aristocratic court system itself, and evaluated as a distant precursor of the warrior governments that would follow.

Only two months after the 'New Emperor' declaration, on February 14, 940, Masakado was defeated by the government army led by Shimotsuke Governor Fujiwara no Hidesato and Taira no Sadamori, and was killed by a stray arrow in Shimōsa Sashima District.

The Kantō independent regime ended in a few months. But the conception itself — of establishing an independent political force outside the control of the central government based on military power — would live on as the prehistory of Japanese warrior-government thought until Minamoto no Yoritomo's establishment of the Kamakura shogunate 250 years later.