Marcus Porcius Cato repeated the above formula ("Carthage must be destroyed") so often in the forum that Carthage was eventually leveled and the spot anathematized. This occurred during the Third Punic War (149-146 BC); that is, the third war between two democracies, or, if you will, two republics.
I bring up the episode because of noises made by John McCain, to the effect that a League of Democracies would ensure world peace: apparently, democracies never go to war. The former -- bellicose -- prime minister of Britain, Tony Blair, had also argued that since democracies don't fight each other, if the whole world were democratic, wars would stop. Notice the premises in the argument:
1) Democracies don't fight each other;
2) If all countries were democracies, wars would stop.
We have already noted that the first premise is historically, and therefore consummately, false. "But before we move onto Athens, we should ask whether European and specifically Greek democracy really was the first democracy of all" (italics original) (Simon Hornblower, "Democratic Institutions in Ancient Greece", ed. John Dunn, Democracy The Unfinished Journey, New York: OUP 1992, p. 2). The author suggests the distinct possibility that democracy was a Phoenician innovation, emulated, like the alphabet, by the Greeks.
"Some historians of Rome have recently argued that it too was really a democracy..." observes John Dunn in the final essay of the book (John Dunn, "Conclusion", p 244). However, he concludes emphatically that Rome was "far from being a democracy", but "for most of its history, from the death of its last king up to the triumph of Octavian, it was indisputably a republic". Since direct democracy is no longer an option in the modern world, we can dispense with such scholarly minutiae and rephrase the first premise to read "Republics and democracies never go to war against each other." Now, that's cutting the Gordian knot.