Final answer:
The burial mounds east of the Mississippi River in the United States were indeed built by a vanished, non-native people known as the Moundbuilders. The Moundbuilders were part of the Mississippian culture, which flourished between 800 and 1600 CE.
Step-by-step explanation:
The burial mounds east of the Mississippi River in the United States were indeed built by a vanished, non-native people known as the Moundbuilders. The Moundbuilders were part of the Mississippian culture, which flourished between 800 and 1600 CE. The mounds served a variety of purposes, including burial sites for the elite, platforms for chiefs and other members of the elite to live on, and centers of worship.