However, prior to the treaty, a group of Shawnee (later known as the Big Jim band) had already left the region to migrate to Texas Territory, then controlled by Spain. Collectively, the band would become known as Absentee Shawnee, as they were referred to as such in the provisional clause of an 1854 treaty regarding Kansas reservation lands. Later, the Texas-Mexico War compelled numerous Absentee Shawnee to leave Texas Territory and to relocate into Indian Territory of Oklahoma. Historians believe that other Shawnee bands, also once in Kansas, had already resettled in Indian Territory beginning around 1839, the year that the Cherokee Nation] were removed from the Southeast to this territory.