The Greeks were only about 7000, maybe 7700, from several cities, so the act of defiance was even greater. But they didn't win, many of them were massacred after 3 days of heroic struggle, fighting to the last men (not only the 300 Spartans).

Things didn't end there. Xerxes and the Persian army managed to burn Athens and only after the naval battle of Salamis were defeated. Well, actually, after that, Athens was again conquered by the Persians under Mardonius. Only with the battle of Plataea (479 BC) they were expelled from Greece.

Yes, I like military and political history.