The Iroquois were unique among indigenous peoples in that they A created an empire
B willingly converted to Christianity
developed a Confederation and a Constitution
D did not practice agriculture

C. developed a Confederation and a Constitution

Explanation:

The Iroquois Constitution, also known as the Great Law of Peace, is a great oral narrative that documents the formation of a League of Six Nations: Cayuga, Onondaga, Mohawk, Oneida, Seneca, and later on, the Tuscarora nations. The date of origin is contested, but it was well before the arrival of European settlers to America.

The six nations of the Iroquois Confederacy, thrive today.

the hereditary right of a monarch to rule from the mandate of heaven