The original Quivirans had moved to eastern Kansas and south to Oklahoma. Their reasons for moving may have been to escape the encroachment of the Apache, whose expansion created war and hostilities among the nations of the Great Plains. It also appears that the Wichita of the 18th century were fewer in number than the Quivirans of the 16th century. It is probable that smallpox and other diseases introduced by Europeans took their toll on the Quivirans as they did on many of the Indigenous people of the Americas.