Complex sentence: It was once home to the Tapajós Indians, a tribe of Native Americans after which the river was named, and the leaders of a large, agricultural chiefdom that flourished before the arrival of Europeans.
Split into simpler sentences: It was once home to the Tapajós Indians, a tribe of Native Americans after whom the river was named. They were the leaders of a large, agricultural chiefdom that flourished before the arrival of Europeans.