Thucydides fought in this war and then wrote it as a possession for later ages: Athens versus Sparta, a twenty-seven-year suicide of the Greek world. He was an Athenian general, exiled after a failure, and he wrote without gods as the engine. Fear, honor, and interest would do. Book 1 is the fuse. He names the truest cause: Sparta’s fear of Athens growing too strong.

A naval island and a rebellious colony drag the two leading cities in. After the Persian Wars, a Greek alliance against Persia had become an Athenian empire, with the treasury moved to the Acropolis. Pericles, Athens’s first man, will not fight Sparta on land. He will sit behind long walls to the sea and live off the fleet. Both sides vote for a war they think they understand. If you want to know how democracies talk themselves into ruin, start here.