Why did Plains Indians develop a sign language, and how did this language relate to how they communicated with other tribes?

Answer:

Responses may vary but should include some or all of the following information: Plains Indians did not have a universal language. Each community spoke different tongues, but trade was still an important part of their society. In order to communicate well with other tribes, they relied on sign language in order to communicate the terms of the trade. This allowed them to carry out ceremonies and trade for goods.