Complex sentence: Feathered war bonnets (also called warbonnets or headdresses) were worn by honored Plains Indian men, sometimes into battle, but most often for ceremonial occasions, and were seen as items of great spiritual and magical importance.
Split into simpler sentences: Feathered war bonnets (also called warbonnets or headdresses) are worn by honored Plains Indian men. They are seen as items of great spiritual and magical importance.