I did some more checking on ancient heresies and discovered that several were very much involved with the original sin controversy. This list was written by a man who is apparently of the Roman Catholic belief, and some of his descriptions may reflect a slight bias.
http://www.ignatiusinsight.com/features2005/kwhthd_ancntheresies_july05.asp
The above site did not mention the Albigensian Heresy which was fought in the 1200s. It has also been called a Crusade, but has nothing to do with the Holy Lands crusades, except as a military learning experience. See this link which does a nice job of listing the important philosophical and historical points.
http://www.the-orb.net/textbooks/crusade/albig.html
I found this very well designed site listing war related death tolls for many different wars worldwide. Multiple references/authors are listed for each topic with their estimates for direct war killing and starvation/disease deaths. For the Albigensian my guess after looking at the various figures is 1/2 to a million, with around 5,000 executed by trial of the Inquisition.
http://necrometrics.com/pre1700a.htm
Conclusions: Wars are terrible things. The European religious war period of from 1559-1715 was extremely fatal. No wonder our founders kept religion out of the Constitution. The Muslim world is undergoing a similar period of sectarian warfare (Sunni vs Shia) and would do well to learn the lessons of history regarding religious wars.
That's why you also had the Reconquista (the defeat of the Moslems in Spain) as a Crusade, you had the Albigensian crusade against Gnostic Cathars and the Northern Crusades against the Baltic pagans
The Sunni-Shia wars have been going on since the 8th century. This is longer and older than the Catholic-Protestant wars.