Born in 1458 into the Amago clan, deputies of Izumo. In 1478 he was stripped of his position and expelled from Gassan-Toda Castle by the Kyogoku overlords. Then in 1484, on the eve of New Year's Day, he led a small force in a daring night raid that recaptured Gassan-Toda Castle—a dramatic reversal that established his reputation for cunning. Over the next two decades he combined intrigue, defection-buying, and military power to extend his influence from Izumo across the provinces of the San'in and Sanyo regions. At his peak he held sway over eleven provinces, making him the dominant power in the Chugoku region. He is ranked alongside Hojo Soun and Mori Motonari as a "Saint of Stratagem." He handed the headship to his grandson Haruhisa in 1537 but retained real influence until his death in 1541 at age 84. After his death, under Haruhisa, the Amago were eventually cornered by Mori Motonari and Gassan-Toda fell in 1566, ending the clan—testament to how much of their power had rested on Tsunehisa's personal genius.