Leaders didn't start to dehumanize opponents in the modern era. You'll find plenty of examples of it throughout history. I picked a more recent example, but I can give you older examples. Some of the "barbarians" that sacked Rome were Arians, a "heretical" spin off from Christianity. If the practice of sacking a city, the whole raping & pillaging deal made a member of an armed force into a barbarian, why weren't Romans ever called barbarians?
But I'm still not clear about your meaning. Are you saying that Plutarch was trying to demonize the Spartans for some reason?
No, history writers aren't the creators of the myths about opponents. There's no good way to know how much of "common knowledge" is true years after its become common knowledge.
I hope you enjoyed the movie. Of course it was a movie, not a documentary.
Yes, I did.
But I think it probably introduced a lot of people to the importance of the battle of Thermopylae.
I think it did too. I couldn't believe my son, a history major had never heard about that battle before I asked him to go to that movie with me.
In the case of the Greeks (which is where the word barbarian comes from), any one who didn't speek Greek was a barbarian because when a non-Greek spoke, it sounded like "bar-bar", simply nonsense. The Greeks did their share of pillaging and raping under the conquests of Alexander the Great. But that doesn't make them barbarians by this definition.
As for the Romans, I haven't studied their word for barbarian. I assume it would have to do with the political organization of the opponent. Those invading Germanic (even if Arian Christian) tribes were not a well-organized empire. But the Roman legions did their share of raping and pillaging. Look what they did to Jerusalem in the late first century AD--they leveled it to the ground. There are many other examples of Rome doing this sort of thing. In this context I don't think barbarian refers to the destructive power of an army.
I think it did too. I couldn't believe my son, a history major had never heard about that battle before I asked him to go to that movie with me.
I am not surprised. The teaching of history is much worse in the high schools. I read recently that school children in London were confused about a statue in that city to Lord Nelson. They thought it had something to do with Nelson Mandella. Those children aren't being taught much about their own history.