Answer: C) Warfare with others.
Explanation:
The earliest known people of Oklahoma were Osage, Quapaq, Caddo Witchita, Waco Tawakony, Comanche, Apache and several other tribes. When the white men started to encroach upon their land it led to constant warfare. Which was a major cause for the decline in their population. Another factor was that they were uprooted to make Oklahoma available for White men after 1865.
