Complex sentence: Mexicans and Americans responded with retaliation attacks against the Apache which were no less violent, and were often indiscriminate, and which fed the fires of a virulent revenge warfare that reverberated back and forth for decades between Apaches and Mexicans and later, Apaches and Americans.
Split into simpler sentences: Mexicans and Americans responded with retaliation attacks against the Apache which were no less violent, and were often indiscriminate. The raiding and retaliation fed the fires of a virulent revenge warfare that reverberated back and forth for decades between Apaches and Mexicans and later, Apaches and Americans.