The Kaskaskia, along with the Peoria, were two of the principal tribes in what was known as the Illinois Confederacy. At the time of first European contact, the tribes of this confederacy held sway over the present area of southern Wisconsin, northern Illinois and along the west bank of the Mississippi River as far south as the Des Moines River in Iowa. By 1700, however, most of the tribes of the confederacy resided in northern Illinois, chiefly on the Illinois River. As a result of continuous war with their northern neighbors, in particular the Sac and Fox Tribes, by the time of the Revolutionary War the Confederacy, represented now by the Peoria and Kaskaskia, was reduced to a fraction of its former strength and had been dispossessed of most of its former territories.
The tribes managed to avoid major conflict with the Americans in both the Revolutionary War and the trouble, which culminated in the Battle of Fallen Timbers and the 1794 Treaty of Greenville. By the Treaty of August 13, 1803, 7 Stat. 78, the Kaskaskia ceded all of their remaining lands in Illinois to the United States in return for protection and patronage. During the trouble associated with the War of 1812, most of the Kaskaskia removed west of the Mississippi to Missouri and Arkansas where they maintained their close relationship with the Peoria. On October 27, 1832, the two tribes signed a treaty, 7 Stat. 403, which gave formal recognition to this union and granted them 150 sections on the Osage Reserve in Kansas.