What made WW1 so special, since it's not the first global conflict and it was not the deadliest war of it's time?

First conflict to be fought worldwide was the 7 years war, it affected europe, america, africa, india, philippines.

And there were other wars that had far more casualties before WW1. For instance, 50 years before WW1 there was a Chinese civil war that killed over 30 million people.
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