Complex sentence: They continued attacking the Cumberland and into Kentucky through the following year, their last raid in conjunction with Dragging Canoe's Cherokee, old animosities left over from the Cherokee-Chickasaw war of 1758--1769 forgotten in the face of the common enemy.
Split into simpler sentences: They continued attacking along the Cumberland River and into Kentucky through the following year, making their last raid together with Dragging Canoe's Cherokee. Former animosities from the Cherokee-Chickasaw war of 1758--1769 were forgotten in the face of the common enemy.