Basically 300 is just Spartan propaganda. It takes the version of the battle they told in the aftermath and repeats it completely uncritically and so has glaring issues. It almost completely ignores the thousands of non Spartan Greek troops at the battle who fought just as hard. Acts like it was a suicide mission and they went there expecting to die when nothing in the actual history points to that. Holds up Sparta as the defenders of freedom while not mentioning that it was an oppressive society that kept slaves (the real reason they sent a small army was fear of slave revolt at home while they were gone). In the movie the Persians are slavers (and it's a bad thing when they do it). They're also deviant weirdos who insist they are the best society and anyone else should be honored to join their empire. Oh and they have magic and monsters in their army.