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Why did Ishida Mitsunari organize an assassination attempt against Tokugawa Ieyasu?

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Statue of Tokugawa Ieyasu in ornate robes holding a bow, with arrows on his back, at the Tosho-gu shrine in Nikko, Japan. — Tokugawa Ieyasu Statue of Tokugawa Ieyasu at the Tōshō Shrine in Nikkō, Japan.

Ishida Mitsunari organized an assassination attempt against Tokugawa Ieyasu because he feared that Ieyasu intended to usurp power from the young Toyotomi Hideyori, the son and heir of the late ruler Toyotomi Hideyoshi.12

Following Hideyoshi’s death in 1598, Ieyasu—one of five regents appointed to govern on Hideyori's behalf—began consolidating his influence through political marriages and by relocating to Fushimi Castle. These actions alarmed other regents and feudal lords, including Ishida, who viewed Ieyasu’s maneuvers as a direct threat to the Toyotomi legacy. In an effort to reassert the authority of the Toyotomi clan and halt Ieyasu’s rise, Ishida formed a coalition of lords and ordered the assassination attempt. When the plot failed, Ieyasu moved to Osaka Castle to act as Hideyori’s protector, further extending his own control and eventually leading to the Battle of Sekigahara.12