Which war was bigger World War 1 or World War 2.?

More British soldiers died in WWI than WWII. However, far more civilians on both sides, and in every theater died in WWII. WWII lasted 2 years longer. The weapons used in WWII were far more lethal, including the A-Bomb. WWII was a war of annihilation of whole groups of people from the Nazi viewpoint. There was genocide in WWI (Armenians), but not on a scale seen in WWII. WWII saw the destruction of entire cities as a policy of fighting the war. The wounded were far more likely to die in WWI. WWI did not involve Asia. [How about Mesopotamia and Palestine?]

It's hard to compare wars. There are many factors, and opinions. However, one way might be to imagine what the result would be if the losing side won. In that comparison, WWII was by far a more threatening war to modern civilization.

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One needs to go a bit further than British casualties ...