> Empires always managed and reshaped migration
Nice moving of goalposts. Meanwhile despite the Russian and Japanese empires, Moscow and Tokyo are 90% [1] and 95.4% [2] native, respectively, and despite the Ottoman Empire, 93.2% of Turkey is either populations native to the region (Turks, Kurds, and Yoruks) or from immediately adjacent regions (Tatars and Azerbaijanis). 95% if we count "Arabs" as adjacent, or even more, depending on what "other" is [3].
That's equivalent to if the UK was 95% English, Welsh, Scottish, Irish, with some French, Germans, Danes, and Swedes. But we're supposed to pretend India and Pakistan moving into England is the same as population exchange with neighbors.
And that's still not "direct causation". But you ignore that, because you want to make it seem inevitable, when it is anything but.
[1] https://en.wikipedia.org/wiki/Moscow#Demographics
[2] https://en.wikipedia.org/wiki/Demographics_of_Tokyo#Multicul...
[3] https://www.britannica.com/place/Turkey/The-central-massif