WW1 was really a European war with some extensions into the ottoman empire. Really it was only the inclusion the British Empire and America which made the forces world spanning.
WW2 on the other hand was truly world spanning with Japan attacking America and Asia and Germany and Italy attacking the whole of Europe, the Balkans and North Africa. If you exclude South America, most of the world was physically at war, rather than just contributing to the war.
Given the scale of the war, losses were relatively lower. If you look at the tables of deaths
WW1 WW2 you notice that the military deaths in WW1 were significantly higher than the the civilian deaths. Yet if we look at WW2, we see that, quite literally, horrific levels of civilian deaths. Most of them nothing to do with the war and everything to do with the way the ware was fought and concentration camps. The Germans didn’t just kill 6 million Jews, they killed Christians and gipsies too. 3 million Polish Christians to go with the 3 million Polish Jews. 11 milion non combatants were killed in 2,000 concentratino camps in Germany.
In WW1 British civilian casualties were 16,000 ish, but the total war dead were around a million. In WW2 Total British casualties were under half a million. A result of more efficient war.
The soviet union, approx. 13 million troops dead approx. 12 million civilians. Dutch east India, 3-4 million civilian casualties…. The major difference between WW1 and WW2 was the number of countries captured in totality and ruled whilst the war raged on at the periphery. Also that both Germany and Japan waged total war on both civilian AND military targets as a shock tactic to force governments to surrender. Equally when the allies retaliated, it was total war. So the Germans lost about 760,000 civilians in WW1 but 3.6 million in WW2 with a total dead of 9m.
The two wars are not really comparable. One was just a much larger and relatively conventional war. The other was thoroughly modern and also thoroughly old fashioned too. Modern in its execution, but old fashioned in how the civilian population was dealt with. Barbaric really.