So revolutions broke out in city after city, and in places where the revolutions occurred late the knowledge of what had happened previously in other places caused still new extravagances of revolutionary zeal, expressed by an elaboration in the methods of seizing power and by unheard-of atrocities in revenge. To fit in with the change of events, words, too, had to change their usual meanings. What used to be described as a thoughtless act of aggression was now regarded as the courage one would expect to find in a party member; to think of the future and wait was merely another way of saying one was a coward; any idea of moderation was just an attempt to disguise one’s unmanly character; ability to understand a question from all sides meant that one was totally unfitted for action. Fanatical enthusiasm was the mark of a real man, and to plot against an enemy behind his back was perfectly legitimate self-defence. Anyone who held violent opinions could always be trusted, and anyone who objected to them became a suspect. To plot successfully was a sign of intelligence, but it was still cleverer to see that a plot was hatching. If one attempted to provide against having to do either, one was disrupting the unity of the party and acting out of fear of the opposition. In short, it was equally praiseworthy to get one’s blow in first against someone who was going to do wrong, and to denounce someone who had no intention of doing any wrong at all.
—Thucydides (translated by Rex Warner)
—found in History of the Peloponnesian War (~430 BC; this translation 1954)