Kobayakawa Hideaki
The Battle of Sekigahara was the biggest and one of the most important battles in Japanese feudal history. It began on October 21, 1600. Initially, the Eastern Army led by Tokugawa Ieyasu had 75,000 men, while the Western Army numbered 120,000 men under Ishida Mitsunari. Ieyasu had also sneaked in a supply of arquebuses. Knowing that the Tokugawa forces were heading towards Osaka, Mitsunari decided to abandon his positions and marched to Sekigahara. Even though the Western army had tremendous tactical advantages, Ieyasu had already been in contact with many of the daimyo in the Western Army for months, promising them land and leniency after the battle should they switch sides, also having secretly communicated with Hideyoshi's nephew, Kobayakawa Hideaki. With a total of 170,000 soldiers facing each other, the Battle of Sekigahara ensued and ended with a complete Tokugawa victory. Later, The Western bloc was crushed and over the next few days Ishida Mitsunari and many other western nobles were captured and killed. Tokugawa Ieyasu was now the "de facto" ruler of Japan.