The author touches on something I've often thought about - the crazy ethnolinguistic diversity within the Austro-Hungarian empire and the fringes of the Russian one.

Consider Lviv - Polish, Austrian, and Ukranian; Catholic, Orthodox, and Jewish. Or, Bratislava: 40% German, 40% Hungarian, and 15% Slovak. The creator of Esperanto, L. L. Zamenhof wrote of the conditions in Bialystok which inspired him:

    The place where I was born and spent my childhood gave direction to all my future struggles. In Białystok the inhabitants were divided into four distinct elements: Russians, Poles, Germans and Jews; each of these spoke their own language and looked on all the others as enemies.

In the aftermath of WWII, the populations within the former Austrian empire became extremely stratified, with the notable exception of Yugoslavia, which retained it's multi-ethnic character.

Now that we have an open Europe, the once-strict are starting to become less meaningful again. I wonder to what extent the populations of Europe will again intermix. Sadly, seeing the Balkans subdivide in to smaller and smaller states does not give one hope.