"Wars had been fought for as far back as anyone could see. They accompanied the first tribes and settlements, and they persisted through the creation of cites, nations, empires, and modern states. They varied only in the means available with which to fight them: as technology advanced so too did lethality, and the unsurprising result that as wars became bigger costs became greater. The first war of which we know the details—the Peloponnesian War between Athens and Sparta during the 5th century BCE—probably brought about the deaths of 250,000 people. The two world wars of the 20th century may well have killed 300 times that number. The propensity for violence that drove these conflict and all those in between remained much the same, as Thucydides had predicted it would, “human nature being what it is.” What made the difference were the “improvements” in weaponry that inflated the body count."