Re WW I, I should probably have used the word "non-nuclear" rather than "conventional." Even so, the admittedly barbaric use of poison gas (not "nerve gas," by the way, a later and more destructive development)along with the bombingj of civilians accounted for only a very few percent of WW I fatalities. About 5% of the 10,000,000 dead in WW I were civilians. In WW II, this percentage was closer to 66% - most of them in Russia and Eastern Europe.