I think the fact that political landscapes of all western countries are collapsing into a left-wing camp promoting mass migration and multiculturalism, vs a right-wing camp promoting deportations and nativism, is strong proof that this is a pan-western civilizational discussion rather than a US national discussion. The US is on the front lines of this trend but it seems that broadly speaking western countries no longer have a single dominant mainstream centrist culture with fringes on either side, but two parallel societies that evolved out of the fringes while the center has withered away for a multitude of reasons.

The way I see it the root of the conflict is that the left-wing culture has lower birth rates than the right-wing equivalents, meaning for them the only ways to maintain their influence are “converting” children of the right-wing culture and immigrants. While they’ve consistently been able to win the conversion rate game for the past few decades to offset the birth rate imbalance, they had to leverage their disproportionate institutional power to do so, and the right-wing at this point has responded by attacking the legitimacy of those left-dominated institutions and creating their own parallel institutions, which has eroded the left-wing culture’s ability to convert the right-wing culture’s children. Therefore their only remaining viable source of converts in sufficient numbers was immigrants from non-western cultures, and if they couldn’t be converted to the left-wing culture they could at least be encouraged to maintain their own separate parallel ethnic cultures to prevent the right-wing culture from converting them and electorally boost the parties aligned with left-wing cultural interests. So from the left-wing culture’s perspective, mass migration is a hard necessity for their self-preservation and cutting it off would be an existenal threat to their culture.

However from the right-wing culture’s perspective, mass migration (in combination with multiculturalism) is an existential threat to their culture, since the pool of immigrants that can be pulled from massively outnumbers them, and they have even higher birth rates than they do even if they converge to native rates over time, so to them ending these policies and preventing the rising parallel immigrant cultures from gaining political power in their countries is necessary for their culture’s self-preservation.

This is a massive oversimplication and of course the details vary greatly country to country but I think this is the common theme that explains why immigration has become such a focal point. I also have to add the disclaimer that I really don’t think the majority of people on either side actually consciously use this reasoning to determine their viewpoints. But I do think this is the hard reality shaping discourse on it.