Between the start of World War One and the end of World War Two, an estimated 90-100 million people died as a result of the conflicts or the regimes connected to them. Those 31 years were almost certainly the most fatal period in human history. Now, 80 years since the end of World War Two, estimates suggest that the number of people old enough to remember the war, who were, say, 10 when it finished and therefore 90 now, ranges from 40-80 million.