After the introduction in Chapter 1, most of Thucydides first book is given over to examining the causes and events leading up to the war. While he describes several diplomatic incidents, Thucydides points out that,
The real cause I consider to be the one which was formally most kept out of sight. The growth and 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 war.
The two Greek power blocks had essentially been fighting a cold war since shortly after the Persian conflict, and each had built up its military assets and financial reserves in anticipation of an eventual war. With both sides primed in this way, it didn’t require much to set them off. Despite this, the Spartans avoided declaring war as long as possible, even when pressed hard by their allies to do something about the Athenian situation. Thucydides blames this on the Spartan culture. As opposed to democratic Athens where risk-taking and quick decision were applauded, the Spartans are conservative and over-cautious. In 1:6 he puts this view in the mouth of a Corinthian envoy addressing the Spartan leaders,
The Athenians are addicted to innovation, and their designs are characterized by swiftness alike in conception and execution; you have a genius for keeping what you have got, accompanied by a total want of invention, and when forced to act you never go far enough. Again, they are adventurous beyond their power, and daring beyond their judgment, and in danger they are sanguine; your wont is to attempt less than is justified by your power, to mistrust even what is sanctioned by your judgment, and to fancy that from danger there is no release.
This is certainly one possible interpretation. However, it is hard criticize the Spartans for wanting to avoid war, or trying to avoid conflict with an aggressive power that had many times their own military budget. The fact is that in our Western literary tradition, particularly since the renaissance, we tend to be heavily biased towards the Athenians. Mostly, this is attributable to the number of works by Athenian authors which have made it into our official Western Cannon. As later writers have striven to make a case for democracy as the one best form of government, an implicit narrative has emerged where the democratic, freedom loving Athenian philosophers fought nobly against the ranks of faceless, fascist, uncultured Spartans. Our high school history texts dwell on the Academy of Athens, but the brutal training of young men in Sparta.
History, as a genre, is about narrative. It straddles the line between literary and non-fiction, because all historic writing tells a story, yet must still conform to known facts.
Ultimately, it was neither the Spartans nor the Athenians who struck the first blows in the war, but some of the second-tier powers to whom they were allied. Things began to get tense when Corinth, allied to Sparta, and Corcyra, a neutral state, went to war over Epidamnus, which each claimed as a daughter colony. Corcyra soon managed to ally herself with Athens, who sent ships to support them. Only the rather convoluted rules of engagement given to the Athenian captains, prohibiting them from engaging Corinthian units unless they tried to land at Corcyra, allowed them to preserve the letter of their treaty with the Peloponnesian League. Reading this section, I was reminded of current events in the paper. The president of Estonia recently published an editorial in the Washington Post about how thrilled he is to have gotten into NATO just before Russia began aggressive operations in nearby Ukraine, because he knows the US and EU are now treaty bound to defend his country. He seems to be right, judging by the recent maneuvers of the 2nd Cavalry a few weeks ago as they helped Estonia “celebrate Estonian Independence Day” 300 yards from the Russian border. We can safely assume that, like those long ago Athenian officers, the US commanders in Estonia have instructions to make a show of force while doing everything they can to avoid actually fighting Russians.
Soon after the Corcyran affair, the several Athenian-aligned cities along the Macedonian border declared independence. Corinth, still bitter over the war with Corcyra, reinforced them. When Athens attacked, Corinth finally had the leverage they needed to convince Sparta that the peace was completely broken. While a formal declaration of war was nearly a year off, there was no longer any possibility of stopping the Peloponnesian War.