The Crisis of the Tumu Fortress, also known as the Tumu Crisis, or the Jisi Incident, was a frontier conflict between the Northern Yuan and Ming dynasties. The Oirat ruler of the Northern Yuan, Esen, captured the Emperor Yingzong of Ming on September 1, 1449.

The Northern Yuan was a dynastic regime ruled by the Mongol Borjigin clan based in the Mongolian Plateau. It existed as a rump state after the collapse of the Yuan dynasty in 1368 and lasted until its conquest by the Jurchen-led Later Jin dynasty in 1635. The Northern Yuan dynasty began with the retreat of the Yuan imperial court led by Toghon Temür to the Mongolian steppe. This period featured factional struggles and the often only nominal role of the Great Khan.