… THE CONSEQUENCES
For Persia and for Greece
The Persians
We don't of course know how Xerxes reacted to his failure to annex Greece to the Persian empire (or even if that's what he was intending to do). Dio Chrysostom, a philosopher who wrote during the 1st century AD, and who knew Persia, said that
It was announced in Persia that Xerxes defeated the Greeks, took Athens and sold into slavery all those people who had not fled and, after this success, imposed tribute on the Greeks and returned to Asia.Dio Chrysostom 11.149
It makes sense that Xerxes would have played down the defeat. And - we have no information otherwise - he could well have issued this sort of propaganda. It would have been important not to spread alarm - and after all, the setback in Greece didn't have any relevance to the existing empire. Dio Chrysostom says that Xerxes needed to "prevent restlessness among the peoples up-country". Building work continued on the royal capital at Persepolis:
By the favour of Ahura Mazda, much that is good did Darius, the king, my father. And also by the favour of Ahura Mazda, I added to that work and built more. [Inscription on coloured glazed bricks from Persepolis]
...and Xerxes ruled for another 14 years. This inscription, of which copies have been found at Persepolis and at Pasargadae, was put up later than the Greek adventure:
By the favour of Ahura Mazda these are the countries outside Persia of which I was king. I ruled them. They paid me tribute. What I told them to do, they did. [a list of 29 peoples follows, including Media, Elam, Armenia, Parthia, Bactria, Babylonia, Assyria, Lydia, Egypt, "Ionians who live by the sea and those who live beyond the sea", Arabia, Thrace, Libyans, Nubians.]

The citadel rock at Van, Turkey; the arrow shows the location of the inscription.

The Xerxes inscription Van citadel, Photos AMW
And this one, 20m up on the rocky citadel of Van, now in Eastern Turkey, shows that Xerxes saw himself as continuing his father's work:
… King Darius,my father, made much that is good, and this niche he ordered to be cut: as he did not have an inscription written, then I ordered this inscription be written. Me may Ahura Mazda protect, together with the gods, and my kingdom and what I have done.
The Greeks: creating "the barbarian"
Soon after they forced the Persians to abandon Greece, the Greek myth-making began. Aeschylus' play The Persians, whose description of the battle of Salamis we've already seen, started the myth which is powerful to this day. The drama reminds the Athenians of their heroic victory at Salamis. It's set in the royal palace at Susa, where the Persian nobles are waiting for news of Xerxes' mighty expedition against Greece. The Queen mother Atossa asks what's so special about the Athenians:

Atossa and Leader from a recent production of The Persians
ATOSSA
What monarch reigns, whose power commands their ranks?
LEADER
Slaves to no master, they call no man king.Awschylus, The Persians 241
Then comes the messenger with the incredible news - they lost! Atossa summons up the ghost of Darius, her late husband, who explains how Xerxes' hybris was to blame. After much wailing, Xerxes himself appears, humiliated, dressed in rags, admitting his terrible mistakes. The play ends in an orgy of uncontrollable grief.
Barbarians
The Greek mind (and the Greek language) liked the idea of pairs of opposites:
- male/female (men were superior to women and should control them)
- men/gods (gods were superior to men and could do what they liked to them)
- master/slave (masters were superior to slaves and could treat them as they wished - though not necessarily badly: they were property after all)
- father/son (sons had to obey their fathers)
- men/animals (men were superior to animals and could use them as they liked - but, like slaves, they could be valuable property)
And, now that they'd shown themselves so superior to the Persians, there was a new one:
- Greek/barbarian
A barbarian was the opposite of a Greek - a negative to his positive. Greeks were starting to define themselves by being "not barbarians".
- Greek: democracy; barbarian: tyranny
- Greek: freedom; barbarian: slavery
- Greek: equality; barbarian: hierarchy - king - royal family - nobles. No voice for common people.
- Greek: simplicity; barbarian: luxury
- Greek: reason; barbarian: emotion
- Greek: honesty; barbarian: deviousness, treachery
- Greek: brave; barbarian: cowardly
- Greek: masculine; barbarian: effeminate
- Greek: disciplined; barbarian: disordered, chaotic
- Greek: austerity; barbarian: extravagance
- Greek: fairness, rule of law; barbarian: cruelty
- Greek: unity; barbarian: jumble of languages, costumes, traditions etc
And so on.
And it wasn't just Aeschylus' play that helped the myth grow.

Temple of Athena Nike (Victory) on the Acropolis, Athens
The Trojan War stories were now spun to look like the Persian War Part I - a previous defeat of Asia by Europe. Soon all Greeks accepted this version - Herodotus sees the war between Persia and Greece as a conflict of civilisations. A mural was painted by Athens' best artist showing the victory of Marathon next to the myths of Theseus and Heracles. A temple of victory (Nike) was built on the Acropolis at Athens - with sculptures showing the battle of Plataea. Where previously artists had shown their skill painting Greeks fighting mythical creatures who symbolised "the other", like Centaurs or Amazons or Cyclopes - from now on it was Persians. Also part of Pericles' building programme, the view from the Gateway to the Acropolis, the Propylaia, was designed by Mnesicles to frame the island of Salamis, scene of the iconic victory, for those exiting the sanctuary.
The barbarian had been invented - and could not be un-invented.

Man v Centaur on a modern Greek stamp
From now on foreigners would not just be enemies: they would be seen as different and inferior. If they were "eastern" they would be seen as exotic, different and inferior - a way that the west has looked at the east ever since. It's sometimes called "Orientalism" - and is a form of racism.