How successful was Xerxes I in the first part of his war with the Greeks?

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Modern scholars estimate that Xerxes I crossed the Hellespont with approximately 360,000 soldiers and a navy of 700 to 800 ships, reaching Greece in 480 BCE. He defeated the Spartans at Thermopylae, conquered Attica, and sacked Athens. However, rising Greek nationalist sentiments conspired to unite the opposition and rob him of his successes.