I always thought it rather one-sided how history teachers always present the Persian Wars as freedom's war against oppression and cruelty.

From Plutarch's Lives of Themistocles, as translated by John Dryden:

When Themistocles was about to sacrifice, close to the admiral's galley, there were three prisoners brought to him, fine looking men, and richly dressed in ornamented clothing and gold, said to be the children of Artayctes and Sandauce, sister to Xerxes. As soon as the prophet Euphrantides saw them, and observed that at the same time the fire blazed out from the offerings with a more than ordinary flame, and a man sneezed on the right, which was an intimation of a fortunate event, he took Themistocles by the hand, and bade him consecrate the three young men for sacrifice, and offer them up with prayers for victory to Bacchus the Devourer; so should the Greeks not only save themselves, but also obtain victory. Themistocles was much disturbed at this strange and terrible prophecy, but the common people, who in any difficult crisis and great exigency ever look for relief rather to strange and extravagant than to reasonable means, calling upon Bacchus with one voice, led the captives to the altar, and compelled the execution of the sacrifice as the prophet had commanded. This is reported by Phanias the Lesbian, a philosopher well read in history.