There's a helot uprising, these Spartan slaves. The Athenians send hoplites to apparently help the Spartans, but the Spartans are suspicious of it and they send them back. And then it culminates with the skirmish you have between Megara and Corinth, which were historically two Spartan allies, but Athens decides to take sides, gets an alliance with Megara. And that's one thing too many for the Spartans, and so they declare war. And you have what's called the First Peloponnesian War, but that's not the Peloponnesian War. That's the first time that you start having a very open conflict between the Spartans and the Athenians. And these conflicts last for on the order of about 15 years, and they're ended with what's called the Peace of 30 Years.