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Britain is a good for example: they (and France) spent the 20th century doing anything and everything to prevent their empires crumbling. One such thing was easing movement of people with their old colonies to maintain influence.
Turns out things can happen without little green men being involved.
I would personally argue that it IS orchestrated, as this massive change happened in 50 years after 1000+ years of no change, but it's not relevant to the actual outcome. Call it a racist conspiracy theory all you want, people are becoming immune to that strategy.
The reason for Japan's (brief) attempt at immigration is they recognised their demographic decline as an actual existential risk. They've chickened out because it proved sufficiently politically unpopular - this is not the same thing. Good luck to them dealing with their demographics in some other as-yet-unknown way.
Yes it's clear you've been drinking the koolaid. And no, people have migrated around for thousands of years, that's simply not grounded in reality. How do you think humans got from Africa to the rest of the planet? Or does that not count as migration because it's somehow too far in the past?
I don't know how else to refer to a conspiracy theory that's primarily driven by fears/hatred of others based not on their merits and values but their ethnicity/race. If you have another preferred term that accurately depicts this I'd be happy to use it instead.