Tink, there is really a lot of information in that article...I picked out two points, including "But every other country is now fully, or fairly close to being fully, ethnically homogeneous." ima suggest it's not the homogeneity, because when diverse people live together for a long time, they can often adapt to each others' customs and develop some common values. At least, that happened where I grew up in SW Washington State; for a long time I assumed we were homogeneous, but then around age 60 I realized there were Native Americans, Middle Eastern Jewish (Dracobly's Clothing Store), Swiss (bells and yodeling every Christmas/Easter), Hispanic, Gypsy, Italian/Greek, and of course them ubiquitous Scandihoovians of which I am one. It worked fine, no crime ever...but hardly anyone ever moved in or out...
So maybe it's more that when new cultures come in suddenly, it can be very disruptive?
The second idea, that of "Even hard-core nationalists liked to talk the language of democracy because it gave them greater credibility internationally as they appeared to be fighting for an ideal rather than for narrow ethnic interests." This, I don't even really grok...outside of my own experience.
And I found Kninjanin's comments interesting!