what you say doesn't change the fact that there'd be more civil wars/fighting in an anarchistic society.
I don't believe this would be the case. Most of the wars of the past century, at least, would have been eliminated if the subjects could secede. One reason I am pro-anarchy is that I am anti-war.
i'm not sure how that changes things. if you are suggesting that the entire world should transition to anarchist systems, which we have no example of, then there would absolutely be power vaccums, which would lead to war.
Is there some reason people can't defend themselves against oppressors without having to oppress others to do it?