Having spent 9 years in the military, I can say with some confidence that even soldiers are not willing to fight a war. War is evil. No one looks forward to it (except the generals). But when its thrust upon you, you rise up to the occasion and defend your motherland.
Some European countries, like Sweden, now have 25% of residents with a motherland which is not the country they live in. Would an Afhan boy living in Sweden fight for Sweden, or would he just take a flight back home to his real motherland? Would an American living in Germany fight for Germany, or take the next flight home? I think we all know the answer, and therefore large parts of the people living on European soil…
Please enlighten us then. If you don't have data or personal experience to share, do you have anything of value to contribute?
Immigrants to nations have fought for their adopted homes with ferocity in the past. It make sense, really - this is somebody who liked (loved, even) the country so much that they worked hard to get there, as opposed to someone who happened to be born there and so is there by default.
Also, one complication to consider in your example of the American in Germany is that US citizens who join foreign militaries risk losing their US citizenship. Of course, for some people that's not a problem (there are a lot of accidental US citizens), but for others and their families it could pose an issue.
https://travel.state.gov/content/travel/en/legal-considerati...