Curt, It all came from a Papal Bull issued over 500 years ago in 1493.  It is still used by our US Supreme Court.  Research the Doctrine of Discovery.  Also watch this video by Bill Moyer as he discuses American Indians and Savage Anxieties with the Indian Lawyer, Robert Williams  at: https://www.youtube.com/watch?v=24IeWTVX840

Basically this Doctrine gave Christian Nations the moral authority to conquer non Christian people and do as they please with them and their land as long as the new colonies were blessed by a Catholic priest.