America is a uniquely diverse country. That's what makes America great.
America has been very lucky, and indeed unique.
When the Europeans got here, there was an indigenous population, but they were rather quickly overrun. If we had a population which was, say, 40% American Indian, we wouldn't be celebrating 'diversity' -- we'd be more like Sri Lanka.
Most of our immigrants were from Europe, and were more civilized than we were. And, fortunately, we got little bits and pieces of Europe: some Italians, some Jews, some Germans, etc etc... So everyone could melt into the pot after a couple of generations. We all looked alike, and were 'Christians', and no one really took their particular brand of 'Christianity' seriously, except as a general cultural thing, which made for a Protestant Catholic divide for a while, but there were never enough Catholics to really make a problem -- if there had been, we might have more tension.
. Even the Jews now have a fifty percent outmarriage rate.
Blacks and whites have not assimilated with each other, sadly. The economic/cultural differences are too great, apparently. So here is our big 'diversity failure'. The Latinoes are somewhere in between ... they seem to be slowly melting into the big mass, but not without plenty of tensions on the way.
And above all, we've been relatively prosperous. A whole continent to exploit, after the original owners were pushed into concentration camps, sorry, tribal areas. No one to threaten us with invasion, so after the Civil War, all our wars were fought elsewhere. After the Europeans devastated each other, we become Top Dog in the world. In 1945 we had not just a plurality, but the majority of the world's productive forces.
Wonderful ... an impregnable fortress-home for liberal democracy, a city on a hill.
Could that change?
You could imagine unlikely (or not) scenarios in which it could: bring in a couple of hundred million people from sub-Saharan Africa, or the Muslim world, and it would for sure.
Plunge us into a long economic depression -- the impetus for the success of the Nazi Party in Germany -- and it might.
Or let the bottom half of the American population, including a substantial white component, come to believe that they are destined to remain relatively poor while the middle class streaks away from them in prosperity -- then you'll have the grounds for a genuine fascist movement.
But probably, we won't suffer much from 'diversity' in the coming decades. We'll always have the "It's all the White Man's Fault" complainers from among the Unsuccessful: it's the path to a successful career, paradoxically, for some people, given the deep liberal desire for self-flagellation.
Our very economic success has given rise to a new generation of future rulers who are utterly self-absorbed, and not ready to become a responsible ruling class. The snowflake generation is going to wreak havoc on our traditional institutions, starting with -- as they already have -- the military. But they'll probably not completely destroy them.
Our real problem is this: we're rapidly (in historical terms) becoming Number Two in the world, and our replacement is a 'Communist' dictatorship that doesn't even use the Latin alphabet. How will we adjust?
Trump's victory is just the first example of how our downward slide is going to give birth to all kinds of bizarre phenomena with unpredictable consequences.
So it's going to be a very interesting 21st Century. No chance of seeing that old Spanish saying, "May no new thing arise" fulfilled.
It won't necessarily be a catastrophe, especially if we can avoid a big war: maybe Iran and China and Russia will become liberal democracies. Then all will be well.
Anyway, 'diversity' is no doubt going to prove to be a problem in the US over the next few decades, especially if we don't have generalized prosperity, but probably not the worst of our problems -- our real problem will be trying to make sure economic prosperity is spread over the broad mass of the population. Given that, we can weather a lot of storms. Without it -- look out!
In fact, we would probably do ourselves a favor, in competition with China which has four times our population, by taking in a hundred million more immigrants over the next decade -- ideally some from here, some from there, as we did with the Europeans -- but taking steps to see that they integrate rapidly, without forming large ghettoes. Look to authoritarian but successful Singapore to see how this is done.