People forget that modern nation states are a very recent, post-democratic construct, and in the past, states competed for people all the time; the fact that these people spoke a different language and had a different ethnicity mattered little to a monarch who themselves might not have belonged to the ethnicity of the country they ruled.
Hence the Prussians bringing Poles to work on the farms in Silesia abandoned by Germans for the factories in the Ruhr, the Russians bringing Mennonites to settle the Volga (of course, it helped that the imperial family was German), the Austrians encouraging Serbs to exchange Ottoman for Habsburg rule, and many more such cases.
Also Germans moving from say Kassel to Hanover or Silesia to Ruhr, or Vienna to Berlin. Very low threshold - same language, culture but lower taxes or better opportunities.
Or Poles moving from Galicia (now Western Ukraine) to Argentina or Chicago.
At the time it wasn't possible to keep citizens tied within borders so higher personal taxes were impractical.
Yes, but I used these examples because these were migrations within Europe where the ethnicity of the migrants were different than where they moved to.
Hence the Prussians bringing Poles to work on the farms in Silesia abandoned by Germans for the factories in the Ruhr, the Russians bringing Mennonites to settle the Volga (of course, it helped that the imperial family was German), the Austrians encouraging Serbs to exchange Ottoman for Habsburg rule, and many more such cases.