2. Japanese their only regret from WW2 from my perspective is LOSING the war.

Other than that, they collapsed when dominating the Mediterranean civilizational zone was no longer enough, and outsiders had grown in numbers and capability enough to pop the bubble.

The period of their greatest success and expansion might be loosely compared to early America. They had an impressive, fusion cultural model to sell, and many bought it. But they also had a common Italic population base that was expanding enough to provide both huge manpower and populations for colonies. It all had the citizenship from the end of the Social War in the early first c BC. The Gauls IIRC got citizenship en masse in the time of Claudius. Of note, culturally variant though they were, the Celts were the closest to the Italics among IE speakers in language and genetics. Spaniards, like the Gauls tended to get a lot of citizenships, for similar reasons, and they also had a lot of Roman colonies among them.

Most other citizenship was handed out on only an individual basis to key elite figures or others on the basis of selection by officials, sometimes towns who had done something to serve Rome, so it did extend beyond Italians at an early date but not in huge numbers. All free subjects in the Empire only got citizenship in 212 with the Constitutio Antonina, a law of emperor Caracalla.

I would suggest no connection whatever with the following huge political, military and economic crises or the decline of the empire.

Rather that the measure was a logical consequence of the evolution of Rome to universal empire, and so were those crises. But I would note that this was not in a period of particular Roman success, nor was there ever again any such thing for the Western empire.

Genetics in the past 15 years seemed to show that the neolithic base of the population of the British Isles is mostly common, there’s still Celtic in the English [they didn't all die or flee to Wales], and there’s plenty of Saxon and Scandinavian in the Celtic fringe.

If anything, Britain and Ireland are more ethnically homogeneous than they are culturally homogeneous.

Or, as I am tempted to do myself, if you want to think of “ethnicity” in slightly more recent than two to five millennia ago terms, then Britain is about as ethnically heterogeneous as it is culturally heterogeneous. That is to say, enough of both to cause plenty of discord but not much of either by world or historical standards.

Just an example, largely true for much of Europe. Mediterranean farmer substrate, varying degree of steppe admixture, then churning about of the resulting ethnolinguistic subcultures for a couple of millennia. A few new adhesions here and there.

That’s pretty homogeneous by any reasonable standard. I find some folks consider it emblematic of Diversity, and therefore use it to justify all modern claims of Diversity regardless of consideration of any matters of degree. By the required standards of our own time, none of the successful Western nations were all that diverse in their times.

Japan does set the gold standard. But as you note their origins- I always giggle a bit when Japanese nationalists complain about the Koreans, or outside observers point out the presence of Koreans as Japan’s most important minority, each in turn to justify their larger claims. It’s true, it’s just that that strikes me as somewhat comparable to comparing Germans or Dutch to the English.

As to what makes the Japanese a success, I expect it’s not the mere fact of homogeneity, it’s that they are homogeneous and Japanese.

In a somewhat recent discussion of crime and policing, some colleagues compared Japan to various other countries doing less well. I forget the details. THe whole question of orderly behaviour versus disorderly was raised. I cavalierly pointed out that some of the distinction probably rested with the fact that the Japanese are Japanese and people X are people X.

Put that way, without need of further exposition, I was surprised to find this was greeted with casual acceptance rather than derision and outrage. I guess everyone isn’t insane yet, not at the basic level.

I think there is much truth in this, and many of our current problems with immigrant assimilation are due to the weakening of the cultural matrix.

However, re Rome: while it is the true that the Roman *empire* was ethnically diverse, was this also true of those who were actually Roman *citizens*? I don’t think I’ve seen any data on this one way or the other.

If you’ve got an overarching cultural matrix to plug into, you don’t need ethnic homogenity. And, I think the “homogenous” nations are at a severe disadvantage for cultural adaptation and flexibility, in general terms. Japan has been an exception, but when you examine all the other homogenous examples, you start to see some different outcomes. I think Japan is an alluring case, but the actual facts of their success are not due to their homogenity, but in other things like an inherent internal flexibility. They’ve been doing this “adaptation” thing since day one, when the first refugees showed up with high technology from China and Korea. The locals happily swiped everything from them, and started the tradition of using whatever cultural and technological innovations came down the pike. Not every homogenous culture does that, or can do emulate them. Japan may well be unique, and to project that homogenity is the reason behind their success is suspiciously convenient. I think it is actually something else, TBH.