Do (incremental) advances in military technology actually change the number of people who die in wars? They might change which people die, or how rapidly, but it seems to me that groups of people who are determined to fight each other are going to do it regardless of what the "best" weapons currently available happen to be. The Mongols wreaked havoc on a scale surpassing World War I with only 13th century technology, and the Rwandan genocide was mostly carried out with machetes. World War I brought about a horror of poison gas, but bullets and explosions don't make people any less dead than poison gas does.

(Although the World War 1 era gases did have one thing that set them apart from other weapons: nonlethal levels of exposure often left survivors with permanent debilitating injuries. Dead is dead, but different types of weapons can be more or less cruel to those who survive the fighting.)