Generally Speaking,what Was a Cause That Led to the Demise

 Generally speaking,what was a cause that led to the demise of the American Indians of the Great Plains?

A) Important minerals and resources,found in areas where Indians lived freely or on reservations.
B) Advancement of settlements as increased populations moved West.
C) All of the answers are correct.
D) Destruction of Indian treaties made earlier.
E) Indian losses in battles and military engagements against American soldiers and settlers.