My armchair impression is that advances in military technology can lead to higher casualty rates when tactics haven't caught up, but that once they do the death toll regresses to the mean pretty quick. Two examples: Minié balls greatly increased the accuracy and effective range of quick-loading small arms (rifling had been around for a while, but earlier muzzle-loading rifles took much longer to load), essentially rendering Napoleonic line tactics obsolete, but it took decades and two major wars (the Crimean and the American Civil War) before the lesson fully sank in. A century later, large-scale strategic bombing of civilian targets contributed to much of WWII's death toll, without bringing about the rapid capitulations it had been intended to produce.