Turning Point - Sekigahara: Toyotomi's Global Expansion and its Consequences

Phase 04 - The Conquest of Kantō

After September 16, outside of the region of Sekigahara, the news of the Western Army's victory and Ieyasu Tokugawa's death spread throughout Japan over a period of about two weeks. Late on the day after the battle, a report arrived at Osaka Castle by a fast horse that had been prepared in advance, stating, "Ishida Jibe Shōfu's army has won a great victory," and the entire Osaka Castle, including Lady Yodo, was elated. The Western Army quickly conveyed to the various Eastern Army commanders that they were free to seize Eastern Army territories, assuming the continued existence of Hideyori Toyotomi.

As the information spread, many daimyō, who had previously been divided between the Eastern and Western forces, began to show a pro-Western stance. Moreover, many Eastern Army forces that had been pushed back by the Western Army accelerated their efforts to negotiate peace and reconciliation with the Western Army. The loss of the larger-than-life figure of Ieyasu had a profound impact on Japan.

However, this was limited to the central regions of Japan, primarily Kinki, Tōkai, and Hokuriku, near Sekigahara. The Western Army intended to thoroughly eliminate hostile forces in this area and had no intention of easing their pursuit.

Although Ieyasu was gone, the Tokugawa clan itself was still intact, and it was believed that stability for both the Toyotomi and themselves could only be achieved through a swift conquest of the Kantō region.

In addition, in distant regions such as Tōhoku, led by Kagekatsu Uesugi and Masamune Date, and Kyūshū, led by Josui Kuroda and Kiyomasa Katō, there was no sign that the battles that had erupted would easily come to an end.

Uesugi, Mogami, and Date, among other northern lords, received the first reports of the results at Sekigahara on September 29, making them among the last powerful military leaders in Japan to hear the news, given the limited speed of information transmission at the time. Even in southern Kyūshū, despite efforts by Josui Kuroda to establish various means of rapid communication with Osaka, such as high-speed ships, there was still a time lag of nearly a week.

Amidst all this, new battles began.

However, there were no major battles in central Japan after that. While there were cases like Kiyosu Castle, where they lost their main commander and put up a desperate resistance, many Eastern Army daimyō began surrendering to the Western Army.

The Western Army advanced along the Tōkaidō with little resistance, easily redrawing the map and advancing to the borders of Tokugawa territory.

Furthermore, good news for the Western Army was coming in during this time.

Osaka Castle had started supplying military funds and provisions to the Western Army's front lines. Additionally, they were able to obtain reinforcements of around 5.000 Toyotomi direct troops in the form of an escort for their transport units. When you included the semi-soldiers involved in transportation, the reinforcements easily exceeded 10.000. As a prior issue, there were cases where daimyō who had previously surrendered to the Eastern Army had joined their ranks, rapidly increasing the size of their forces.

And at this point, following Hideyoshi Toyotomi's strategy, the Western Army had finally established a long-term warfare system by transporting a large quantity of supplies into Owari.

Moreover, by this time, Hidetada Tokugawa's forces, which had turned back on the Tōkaidō, were retreating to Kantō without any interference from the Western Army, allowing the Tokugawa clan to still maintain a significant military presence.

While the 30.000-strong Tokugawa main force at Sekigahara had scattered, there were still over 50.000 Eastern Army troops primarily concentrated in the Kantō region.

These forces were expected to mainly engage in castle defense battles in the future, targeting the exhausted Western Army for a decisive battle in Kantō.