As for the ongoing extinction of cultures and languages, one word: urbanization. Young people can't find a decent job around home, so they move to big cities where the neighbours don't understand their language, and think speaking it makes you a hick. That works to the advantage of both "Western culture" and "Arab/Sunni Islam", but the homogeneizing effect of the massive spike in urbanization that we're living through would be much the same if neither existed.
]]>Russia in 1910 included all of the former Soviet Union plus Finland and a large chunk of Poland. Wikipedia suggests that the population of the former USSR on its own is 292 million; Finland adds another 6 million, and Poland has 37 million, of whom I'd guess more than a third probably live in what used to be the Russian part. So a like-for-like comparison would be ~150 million in 1910 vs. ~310 million today.
Of course, world population has considerably more than doubled since 1910, so this is still lower than you might expect - but it's not ZPG either.
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