Thucydides on revolution in the cities

So bloody was the march of the revolution, and the impression which it made was the greater as it was one of the first to occur. Later on, one may say, the whole Hellenic world was convulsed; struggles being everywhere made by the popular chiefs to bring in the Athenians, and by the oligarchs to introduce the Lacedaemonians. In peace there would have been neither the pretext nor the wish to make such an invitation; but in war, with an alliance always at the command of either faction for the hurt of their adversaries and their own corresponding advantage, opportunities for bringing in the foreigner were never wanting to the revolutionary parties.

The quote: The sufferings which revolution entailed upon the cities were many and terrible, such as have occurred and always will occur, as long as the nature of mankind remains the same; though in a severer or milder form, and varying in their symptoms, according to the variety of the particular cases. In peace and prosperity states and individuals have better sentiments, because they do not find themselves suddenly confronted with imperious necessities; but war takes away the easy supply of daily wants, and so proves a rough master, that brings most men's characters to a level with their fortunes.

Revolution thus ran its course from city to city, and the places which it arrived at last, from having heard what had been done before carried to a still greater excess the refinement of their inventions, as manifested in the cunning of their enterprises and the atrocity of their reprisals. Words had to change their ordinary meaning and to take that which was now given them.