Yesterday, I noted that according to Socrates the Kallipolis has permanent natural would-be-friends and permanent, natural would-be-enemies (see also the long quote from the Republic). Inserted in this analysis is his a call for the natural would-be-friends to treat each other with (what we might call) humanity in war and to promote fraternity among them (presumably also outside war). In fact, in its dealings with its natural would be friends, the Kallipolis is supposed to "correct them, then, for their own good, not chastising them with a view to their enslavement or their destruction, but acting as correctors, not as enemies.” (Republic 471a) So, among the natural, permanent friends, the Kallipolis should act a kind of moral beacon or political exemplar that can guide political reform.
One might wonder (i) who the natural allies of the Kallipolis are, and (ii) what makes a natural friend and natural enemy, and (iii) why Socrates rejects the possibility of fluid political alliances in foreign affairs. Now, on (i) Socrates is explicit: the permanent natural allies of the Kallipolis are the fellow Greeks (470c). Anticipating Machiavelli (in the closing page of The Prince), Plato inscribes in his text a call for a form of political unity that transcends both the best realizable polity itself and then present political realities (which is one of political war among the Greeks). And this political unity is characterized (as I noted in the previous paragraph) by a kind of spiritual hierarchy in which the Kallipos is first among equals. Socrates gives an instrumental reason for such permanent unity, namely, to prevent being being enslaved by barbarians (469c; in this instance the Persians).
Now, as Socrates makes explicit (i) presupposes that the inhabitants of Kallipolis are going to be Greek (470e). So, this is a clear rejection of what we could multi-nationalism/culturalism (of the sort that Plato's Laws does explore). The reader of the Republic has to confront here the question whether Socrates's position is chauvinist: that other national/ethnic/linguistic (etc.--I return to below) cultures cannot have their own Kallipolis. Because of the use of 'barbarian,' my students assumed that Socrates is such a chauvinist that only one kind of people are culturally or ethnically capable of philosophical polity. (I have a tendency to interpret Aristotle as a cultural/national chauvinist.) My own reading of Socrates is (recall this post on 592) that his position, while perhaps rhetorically drawing on shared sense of cultural superiority, does not require such national/cultural superiority, and that a non-Greek Kallipolis elsewhere is, in principle, possible.* As it happens, I think Locke's views on toleration are structurally similar; we tolerate in virtue of our shared protestant theism; others (born say in Istanbul) may tolerate in virtue of their shared theism, etc.
Socrates does not really explain what makes a natural friend. But he does provide sufficient hints to offer an account for (ii). In addition to shared language, and, perhaps, sense of people-hood, a key binding factor is what we would call religion or religious practices. This is signaled by Socrates, when he asserts that how to treat fallen Greek soldiers (temporary enemies), is not up to philosophy, but rather should be inquired from “Apollo then, how and with what distinction we are to bury men of more than human, of divine, qualities, and deal with them according to his response." (469a) I am not suggesting religion is the only consideration at play: Socrates is keenly aware that ordinarily soldiering is done, in part, for profit (because the fallen enemies are a source of material goods). But Socrates emphasizes that what the Greeks have in common is something religious.+
And, in fact, Socrates had explicitly noted that the founding of Kallipos would have to defer to the instructions of Appolo:
“For us nothing, but for the Apollo of Delphi, the chief, the fairest and the first of enactments.” “What are they?” he said. “The founding of temples, and sacrifices, and other forms of worship of gods, daemons, and heroes; and likewise the burial of the dead and the services we must render to the dwellers in the world beyond to keep them gracious. For of such matters we neither know anything nor in the founding of our city if we are wise shall we entrust them to any other or make use of any other interpreter than the God of our fathers. For this God surely is in such matters for all mankind the interpreter of the religion of their fathers who from his seat in the middle and at the very navel of the earth delivers his interpretation.” [427bc]
Kallipolis is explicitly part of a political-theology in which deference is shown to the pre-existing religion. This is especially so in matters of rites and worship. Of course, this religion is cleansed from immorality and internal contradiction by the censorship laws of Kallipolis. So, one sense in which Kallipolis is a beacon to other Greek cities, is in having an improved version of the stories and symbols associated with the pre-existing religion. And the Greek natural friendship is constituted by this shared theological horizon.**
I suspect that absent true religious innovation, the boundaries of religious communities explain for Socrates why (iii) there are social groupings that are natural friends/enemies. Religion and political groupings are on this account mutually supportive in creating coherent enduring political bonds of friendship, and enduring possible enmity. Even those of us that do not accept clash of religious ethno-national civilizations have to take Socrates's position seriously.
+In Shorey's translation the commonality are religious holy sites (where the oracles are); 470.
**The quoted passage implies that the the Greek god is the God of all people. This is a form of cosmopolitanism that is not reflected in the treatment of natural enemies/friends..