Complex sentence: Even after the revolt of the young chiefs of the Upper Towns, the Lower Towns were a major voice, and the "young chiefs" of the Upper Towns who dominated that region had themselves previously been warriors with Dragging Canoe and Watts.
Split into simpler sentences: Even after the revolt of the young chiefs of the Upper Towns, the Lower Towns were a major voice. The "young chiefs" of the Upper Towns had previously been warriors with Dragging Canoe and Watts.