Complex sentence: Cochise and the Chokonen-Chiricahua lived in the area that is now the northern Mexican region of Sonora, New Mexico, and Arizona, which they had moved into sometime before the coming of the Europeans.
Split into simpler sentences: Cochise and the Chokonen-Chiricahua lived in the area that is now the northern Mexico. In the region of Sonora, New Mexico, and Arizona, which they had moved into sometime before the coming of the Europeans.