Make your decision with the slow deliberate care due to important matters, and don't bring trouble on yourselves by giving in to other people's opinions and complaints. Before you go to war, you must realize how unpredictable war is. The longer it lasts, the more it is likely to turn on chance. The odds of disaster are the same for both sides, and no one can see where the dangers lie…. So, while it is still possible for both sides to use good judgment, we ask you not to dissolve the treaty or breathe your oaths, but to submit our differences to arbitration according to the agreement. If not, the Gods who heard the oaths are our witnesses, and once you have started the war, we will do our best to resist wherever you show the way (I: 78).

Nevertheless, despite this rather magnanimous offer, Sparta continued to remain antagonistic toward Athens. Their King, Archidamus, warned the council that there was no income available for war, that Sparta had appropriate sea power, and that the war would last generations if they allowed it to happen:

But do not take arms just yet. Send to them instead, and make demands…. And use the time to prepare our forces. We should acquire allies…...

If Athens accepts our demands, so much the better; if not, we'll let two or three years go by and then attack them, if we choose, from a stronger position. And perhaps once they've seen our preparations, and realized that we really do mean to back up our demands, they'll give in more easily… (I: 82).
However, despite this wisdom, and the fact that members from both sides suggested ways to prevent the way, the majority of the Spartan council voted to go to war, and called for a formal meeting of all the Peloponnesian League, which resulted in a Spartan attack. However, clearly seeing that Athens had backed Sparta into a corner, "The main reason the [Spartan's} voted… that the war should begin was not the allies' speeches… [it was] because they were afraid Athenian power would continue to grow, seeing that most of Greece was already subject to them" (I: 88).

Source:

Thucydides, trans. with notes by Paul Woodruff. (1993). On Justice, Power, and Human Nature: The Essence of Thucydides' History of the Peloponnesian War.

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