> homogenous country

This must require a shocking cultural adaptation. In the US, we have many social bonding customs. You'll hear often about how Americans strike up conversations at random, often say "how are you?" as a default greeting, and smile a suspicious amount. There are dozens of examples, but that's because it's baked into the culture of USA as a foundational aspect. I can't imagine trying to shift from essentially Japan to America++ in two decades.

Where you happen to be born is the only criteria for population diversity?

right but the entire norwegian society and its welfare state was built upon that homogeneity, where everyone and their neighbor looked "familiar" and could be implicitly trusted to share the same customs. As the foreign born population grows, Norway has taken many steps to restrict immigration, asylum claims, and benefits to immigrants. public opinion has shifted (though not dramatically) as well. parent poster's claim of "easy mode" is receding, so it's not like norway has found a solution to "being a generous welfare state while also openly welcoming foreigners".

How much of that is from legal migration from developed first world countries for both countries?

I know I will be downvoted for this.