Thucydides book 1, chapter 23:

The Median war, the greatest achievement of past times, yet found a speedy decision in two actions by sea and two by land. The Peloponnesian war was prolonged to an immense length, and long as it was it was short without parallel for the misfortunes that it brought upon Hellas. [2] Never had so many cities been taken and laid desolate, here by the barbarians, here by the parties contending (the old inhabitants being sometimes removed to make room for others); never was there so much banishing and blood-shedding, now on the field of battle, now in the strife of action. [3] Old stories of occurrences handed down by tradition, but scantily confirmed by experience, suddenly ceased to be incredible; there were earthquakes of unparalleled extent and violence; eclipses of the sun occurred with a frequency unrecorded in previous history; there were great droughts in sundry places and consequent famines, and that most calamitous and awfully fatal visitation, the plague. All this came upon them with the late war, [4] which was begun by the Athenians and Peloponnesians by the dissolution of the thirty years' truce made after the conquest of Euboea. [5] To the question why they broke the treaty, I answer by placing first an account of their grounds of complaint and points of difference, that no one may ever have to ask the immediate cause which plunged the Hellenes into a war of such magnitude. [6] The real cause I consider to be the one which was formally most kept out of sight. The growth of the power of Athens, and the alarm which this inspired in Lacedaemon, made war inevitable. Still it is well to give the grounds alleged by either side, which led to the dissolution of the treaty and the breaking out of the war.

downloaded from http://www.perseus.tufts.edu/cgi-bin/ptext?lookup=Thuc.+1.23.1