Hmm. I think US-USSR / Athens-Sparta is a poor analogy. They spoke the same language, and it’s a two day walk. I’m going to defer to Athenians on the character of Sparta over modernish debunkers.
The best and most recent example of that, for a modern American, would be the USSR. You do come across similar processes with, say, Chinese or Arabs, but they're not explicit enemies, and there's more cultural integration and exchange in those cases.