The Eastern Army Vanguard at Sekigahara: Why Masanori, a Toyotomi-Loyal Warrior, Sided with Ieyasu

On October 21, 1600 (the fifteenth of the ninth month of Keichō 5), at Sekigahara in Mino Province.

The Eastern Army of 74,000 led by Tokugawa Ieyasu faced the Western Army of 82,000 led by Ishida Mitsunari.

Cutting the first charge of the Eastern Army was the Hideyoshi-raised warrior Fukushima Masanori.

He was thirty-nine. The paradoxical structure of Masanori — supposed to be a retainer of the Toyotomi house — first striking the Toyotomi's senior retainer Mitsunari was already embedded in this day's Sekigahara.

The conflict between Masanori and Mitsunari became decisive in the leap third month of 1599, the year before Sekigahara.

Toyotomi Hideyoshi had died the previous year, and within the regime the conflict between the administrator faction including Ishida Mitsunari and the military-merit faction including Katō Kiyomasa and Fukushima Masanori intensified.

In the leap third month of 1599, an incident occurred in which Mitsunari was almost attacked by Tokugawa Ieyasu at Fushimi.

The initiative for the attacking side was the seven generals: Katō Kiyomasa, Fukushima Masanori, Kuroda Nagamasa, Asano Yukinaga, Ikeda Terumasa, Hosokawa Tadaoki, Katō Yoshiaki.

By Tokugawa Ieyasu's mediation the incident was settled, but Mitsunari fell from grace and withdrew to Sawayama Castle.

Thereafter, Masanori, at the core of the seven generals, became substantively the central figure of the anti-Mitsunari faction.

That Masanori sided with the Eastern Army at Sekigahara in 1600 was not simple support for Ieyasu.

It was rather participation in war based on the self-recognition of 'protecting the Toyotomi house from Mitsunari.

' Other Toyotomi-loyal warriors — Kiyomasa, Asano Yukinaga, Kuroda Nagamasa — joined the Eastern Army by the same logic.

This structure of 'Toyotomi-loyal warriors making the center of the Toyotomi regime, Mitsunari, the enemy' made possible Ieyasu's seizure of the realm.

In the pitched battle at Sekigahara, Masanori as vanguard of the Eastern Army first charged the Ukita Hideie corps of the Western Army center, and created the current of Eastern Army advantage.

After Sekigahara, Masanori was moved by Tokugawa Ieyasu from Owari Kiyosu at 200,000 koku to Aki-Hiroshima at 498,000 koku, an increase in fief.

As a reward for Sekigahara it was one of the maximum-class dispositions. But this increase was also a measure that positioned Masanori as a tozama daimyō under the Tokugawa regime.

Ironically, the peak of Masanori's glory as a Toyotomi-loyal warrior was given as a result of his own labor in weakening the Toyotomi house.

This structure would define the fate of Masanori's later years, over the following nineteen years, until the Hiroshima forfeit of 1619.