After a devastating battle of 9 September 1730, in Illinois, in which hundreds of warriors were killed and many women and children taken captive by French allies, Fox refugees took shelter with the Sac. This made them subject to French attack in turn. The Sac continued moving west to Iowa and Kansas. Keokuk and Black Hawk were two important leaders who arose among the Sauk. At first Keokuk accepted the loss of land as inevitable in the face of the vast numbers of white soldiers and settlers coming west. He tried to preserve tribal land and his people, and to keep the peace. Having failed to receive expected supplies from the Americans on credit, Black Hawk wanted to fight, saying his people were "forced into war by being deceived". Led by Black Hawk in 1832, the mainly Sac band resisted the continued loss of lands (in western Illinois, this time.) Their warfare with United States forces resulted in defeat at the hands of General Edmund P. Gaines in the Black Hawk War. Oklahoma history
About this time, one group of Sac moved into Missouri, and later to Kansas and Nebraska. In 1869, after the Civil War, the United States forced the larger group of Sac to move into a reservation in Indian Territory (now the state of Oklahoma). They merged with the Meskwaki as the federally recognized Sac and Fox Nation. (The United States had been making treaties with the two tribes together since their residency in the Midwest.)
The Sauk/Sac called themselves the 
autonym of Othâkîwa, Thâkîwa, Thâkîwaki or Asaki-waki/Oθaakiiwaki people of the yellow earth [("people coming forth [from the outlet]," i.e., "from the water")], which is often interpreted to mean "yellow-earth people" or "the Yellow-Earths", due to the yellow-clay soils found around Saginaw Bay. This interpretation possibly derived from the Sauk words Athâwethiwa or Athâw(i) ("yellow") and Neniwaki ("men, people"). This was later shortened to "Asaki-waki". In addition, the Fox (Meskwaki) were generally known among neighboring tribes as the "people of the red earth" - the Sauk and Fox also used this term: Êshkwîha or Meshkwahkîha ("people of the red earth"). Some Ojibwe oral histories also place the Sauk in the Saginaw Valley some time before the arrival of Europeans. Sauk traditions state that the tribe occupied the vicinity of Saginaw river. (In this tradition, the name Saginaw comes from the Ojibwe "O-Sauk-e-non," meaning "land of the Sauks" or "where the Sauks were.") Approximately from the years 1638 to 1640, it is believed that a fierce battle ensued, nearly annihilating the entire Sauk Tribe. The story goes that the Chippewa inhabited the lands north of the Saginaw Bay, and the harsher northern climate caused more difficulty in prosperity compared to that of the Sauk occupying the area of Saginaw Valley. The Chippewa allied with the Ottawa, who resided south of the Sauk, and sprung a series of attacks on the Sauk Tribe which practically decimated their people.