Educated atheists I don't think would go along with your historical timeline; to think the following of Christ came about ~300A.D. wouldn't be held by anyone with a high school World History understanding.  Beyond the Bible, other histories show it as a live movement pretty much to the full extent of the Roman Empire by 300....  The main doctrine of Christian church is there is NOT purity of soul but original sin that maintains itself even amongst those who are converted and become believers.  From what you have written here, I think you need to become familiar with U.S. Government's Bill of Rights and early colonial history before sparking off talk on 'melding of religion and government'.  History has many strands, and the Christian Church in many ways has improved "Natives" lives.  (Also go back and review Native tactics, torure, slay and beatings among the various tribes and you will find that such sins are universal in world cultures and certainly American History).