Here are three trends that are often discussed in isolation:
The low birth-rates of advanced economies
The rise of a xenophobic anti-immigration politics
The fragility of the welfare state
While these subjects might seem to have nothing to do with each other, in fact they crash into each other like dominos. As rich countries have fewer babies, they need immigration to grow their prime-age workforces. But as the foreign-born share of the population rises, xenophobia often festers and threatens egalitarian policy-making.