In the Battle of Sekigahara in 1600, the Hosokawa family took part in battles in three regions of Sekigahara, Tango Tanabe-jo Castle and Bungo Kitsuki-jo Castle, but Okinaga, following Tadaoki, went on an expedition against Aizu and to the Sekigahara battle field.
慶長5年（1600年）の関ヶ原の戦いでは、細川家は、関ヶ原、丹後田辺城、豊後杵築城と三方面で戦闘したが、興長は忠興に従って会津征伐、関ヶ原の戦いへ赴いた。