In 1600, when the Battle of Sekigahara broke out, as the head of the Hosokawa clan, Tadaoki HOSOKAWA declined the invitation of Sei-Gun (western camp, led by Mitsunari ISHIDA) to join them, and instead his army sided with To-Gun (eastern camp), which was headed by Ieyasu TOKUGAWA.
1600年（慶長5年）関ヶ原の戦いが勃発すると、当主になっていた細川忠興は石田三成率いる西軍の誘いを退け、徳川家康率いる東軍に加勢した。