In 499 B.C.E. the Greeks who lived in Ionia unsuccessfully rebelled against the Persian Empire, which had ruled the area for fifty years (see Chapter 2). The Athenians provided halfhearted help to the Ionians, and in retaliation the Persians struck at Athens, only to be surprisingly defeated by the Athenian hoplites at the Battle of Marathon. In 480 B.C.E. the Persian king Xerxes (ZUHRK-seez) personally led a massive invasion of Greece. Under the leadership of Sparta, many Greek poleis, though not all, united to fight the Persians. The larger Persian army enjoyed early success, but the tide quickly turned and the invasion ended in failure.

The victorious Athenians and their allies then formed the Delian League, a military alliance intended to liberate Ionia from Persian rule and keep the Persians out of Greece. The Athenians, however, turned the league into an Athenian empire. They reduced their allies to the status of subjects. Athenian ideas of freedom and democracy did not extend to the citizens of other cities, and cities that objected to or revolted over Athenian actions were put down.

Under their great leader Pericles (PEHR-uh-kleez) (ca. 494–429 B.C.E.), the Athenians grew so powerful and aggressive that they alarmed Sparta and its allies. In 431 B.C.E. Athenian imperialism finally drove Sparta into the conflict known as the Peloponnesian War. The Peloponnesian War lasted a generation (431–404 B.C.E.) and brought in its wake disease, widespread civil wars, destruction, famine, and huge loss of life. In 404 B.C.E. the Athenians finally surrendered to Sparta and its allies, and Sparta stripped it of its empire. Conflicts among the states of Greece continued, however.