The Seneca, Seneca, Oneida, and Oneidas are all part of the Five Nations, a confederacy of Native American tribes located in the Northeastern United States. The Seneca were the largest and most powerful of the Five Nations, and the Oneida were the smallest. The Seneca and Oneida were two of the original five nations that formed the Iroquois Confederacy in the 16th century. The other three nations were the Mohawk, Cayuga, and Onondaga. The Seneca and Oneida were also two of the six nations that formed the Haudenosaunee or Iroquois League in the 18th century. All four of these terms, Senecas, Seneca, Oneida, and Oneidas, refer to one of the five nations that make up the Iroquois Confederacy.