"When you march up to attack a city, make its people an offer of peace ... This is how you are to treat all the cities that are at a distance from you and do not belong to the nations nearby. However, in the cities of the nations the Lord your God is giving you as an inheritance, do not leave alive anything that breathes." (Deuteronomy 20:10-16)
The wars of Israel in the Old Testament are difficult to reconcile with the nonviolence of Jesus, there is no doubt about that. But an honest reading requires we observe that, even so, scripture recounts YHWH commanding Israel to place territorial limits on the cherem, the wars of destruction. However brutal it sounds to modern ears, Moses made clear that the cherem was limited to cities (that is, the cherem exluded the peasant class who stood apart from the military class) and limited it to the land of Caanan (that is, the cherem excluded Pagan cities beyond Palastine). So whatever else we may say, as Christians or non-Christians, we must reject the claim that the Old Testament provides a universal mandate for genocide. It is clear then, that if Christians were ever to justify such brutality in different wars in different lands, they go beyond scripture, Old Testament as well as New Testament.