Xerxes, who was Darius' son declared war on Athens/Greece. He did this for revenge because his father died of embarrassment from the last war. One very important battle in this war was the battle of Thermopylae. 7000 Greeks, including 300 Spartans, try to stop the Persians. The Spartans fight the Persians for 3 days so the others can go warn the city-states so they can prepare. The Spartans died but they helped Athens win the war.