In 1203, How Tokimasa Made Shikken Politics

At the end of August 1203 (Kennin 3), at Kamakura. The second shōgun Minamoto no Yoriie (then twenty-one, Tokimasa's grandson) fell to a sudden illness.

Kamakura shogunate internal politics tightened rapidly over the succession to Yoriie.

At the time, Tokimasa was in a supporting position at the shogunate Mandokoro Bettō office, and was also linked with Yoriie's mother Masako (Tokimasa's daughter).

Taking this illness as the opportunity, Tokimasa moved to fundamentally reorganize the power structure of the shogunate.

Tokimasa confined Yoriie to Shuzen-ji (in the modern Izu City, Shizuoka Prefecture) and substantively excluded him from the shōgun office.

He suppressed the Hiki clan of Yoriie's supporters in September (the Hiki Incident), purging the anti-Tokimasa faction within the shogunate.

In October 1203, he raised up Yoritomo's second son Sanetomo (then twelve) as the third shōgun, and took himself the office of Mandokoro Bettō (in substance the top executive office of the shogunate).

From then on, this office would come to be called 'shikken.

Tokimasa's assumption of Mandokoro Bettō was a watershed institutional creation in Japanese political history.

A double structure in which the shōgun is held as symbolic apex, while the real power is held by the shikken.

Thereafter, in the Kamakura shogunate, nine generations of Hōjō shikken would hold the real power, and the shōgun office would become nominal.

This structure left its influence even on the relationship of 'shōgun and elders (rōjū)' in the Edo bakufu, and became the prototype of the 'separation of symbol and real power' in Japanese warrior government.

Tokimasa's personal decision of 1203 defined the political structure of Japan for over six hundred years.

The 1203 removal of Yoriie was realized not by Tokimasa alone, but by joint combat with his daughter Masako.

Masako, while the real mother of Yoriie, supported her father's decision to remove her son.

It was a political judgment prioritizing the survival of the Kamakura shogunate over the mother-son relationship.

The 'Hōjō executive committee' of the three — Tokimasa, Masako, and Yoshitoki (Tokimasa's son) — made the governance structure of the subsequent Kamakura shogunate.

Masako would later, as the 'Nun-shōgun,' play a decisive role in the Jōkyū War (1221).