When the enemy got a foothold this type of thing became way more common. Before then there was no such thing being repeatedly done, the only wars going on in northern and western European lands in the Celtic sphere was over tribal disputes. Before the chiefs fought they had to consult druids to defer whether or not war was the spiritual answer to the problem as Druids had a higher 'rank' and the final say-so spiritually.
The emphasis on conflict and sacrifice of much life for definitive borders and political ends came about with the Roman conquests. That's why our society has developed on non-spiritual lines and different from the Gods, whereas that was the direction in which the Celts were going in with their society.
The whole thing is a result of revanchism in an emotional and identity sense, not a territorial one. Between familial bonds and kin instead of nations which didn't really exist in the same way they do today. Fighting back one another with even more viciousness and destruction both ways until it became insurmountable and marked on the consciousness of future generations which then were totally swept up and then with the jews in tow, became alright with it thinking bloodshed was normal.
All pagans have never had an inclination for mass sacrifices and even with the Aztecs and related its clear the enemy had physical control over them at some point and probably jews there as well. The Aztecs after the enemy left them, and being non-European took it as a definitive culture and were probably confused, thought the pyramids they had were given by the enemy influence and not ours. With Europeans, this same process was ongoing during the Dark Ages but we fought back against it hard in a total way to where now we are even discovering new things for ourselves without ancestral knowledge. The enemy couldn't come face to face with Europeans in the same way for spiritual reasons, going into total war with us meant the Gods on our side too and also if certain liable things were to occur in such a timeline, would spell their doom and failure on this planet even quicker. War leads to that kind of a struggle, where individual advancements maximise and peak to combat the downpull that war is. Advancement then sometimes has to happen unnaturally like in the case of nuclear bombs and other nasty inventions.
Conventions like major torture methods and other extreme stuff is an 'advancement' in revenge taking, blood revanchism and anger that then ends up misdirected against ones folk instead of the enemy who if people then had the ability to discern, were the only core factor in the discrepancies and conflicts of the day. The nature of man is proud and energetic, not weak and confined. Those who preached and wrote doctrines of the latter hired the proud and energetic with Rome's stolen money, to kill the other strong peoples and instil weakness across the board in an ironic fashion.
The one remaining detail? It's the weak i.e the enemy jews doing the killing in the first place by abusing the powers of the stronger and more organised peoples against others. The real evil occurs in the foundation upon which massacres are justified in the first place, which is within the spiritual.
Gentiles have committed atrocities, but not to the extent the enemy has and will always so long as they are given that hook line inside our affairs. That's simply the nature of it, the only reason we have done in the first place is due to that hook of the enemys.