The Chickasaws and Choctaws once were one people, according to the Chickasaw migration story. This understanding is common to the accounts of English trader James Adair in 1775 and the 20th century Chickasaw activist, Jess Humes.
There are other versions in between. They all involve people making a lengthy journey from the west, following a sacred leaning pole, and a complication that resolves when the people split into two groups.
In the Chickasaw versions, one group stays put at the behest of a leader named Chata. The other, much smaller group, follows his twin brother, Chikasa, as they continue heading east. Was this a simple yet profound difference of opinion on this one matter? A case of sibling rivalry? Or had the seeds for the split already been planted, possibly through differences among clans?
Before these highly spiritual people separated, a prophet may have foreseen the eventual warfare between them, and warned that it would be caused by a greedy and hateful alien race. Such a premonition would have added even more distress to the parting.
Whatever, that moment of separation marked the emergence of two distinct peoples. Before they split up, the migrants had a name we will never know. Afterward, they adopted the names of their respective leaders and became the Choctaws and Chickasaws.
When the division occurred is a mystery that will never be solved. But the point is that the break up was permanent.