Unchecked immigration caused massive crashes in wages where they showed up, leading to locals suffering economic hardships. Since the immigrants didn’t mind being paid less than their peers because they were new and broke, employers preyed on them for cheap labor.
Cue “they took urrrr jawbbsss”
Also, immigration can a cause a serious decline in local food supply if not carefully managed.
And lastly, some nations are extremely broken politically and logistically. There are some nations where crime is not policed at all. Those people flee to another nation for a safer life, but some of the behaviors they think are mild are downright felonies in their new hosts. Which then causes “economic flight” where wealthy taxpayers abandon areas with high immigration quotas to avoid having to argue over what is safe or tolerable. They just move to where it is not tolerated, rather than stay and help through compassion and charity.
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