Japan is a pioneer and an extreme version of where much of the First World is headed as longevity increases and fertility declines. The likely consequences are slower economic growth, reduced innovation, labor shortages and huge pressure on pensions. If you think our entitlement politics are fraught, think about this: In Japan in 2050, the old-age dependency ratio — the number of people 65 and over as a percentage of the number who are 15 to 64 — is projected to be 71.2 percent.

The comparable figure for the United States is 36.4 percent, up from 25.7 percent in 2020. Still high, but if it proves manageable, we will have immigration to thank. America still attracts dynamic, hard-working people from around the world, and they and their offspring help keep our population and our economy growing, as recent Pew Research Center and International Monetary Fund papers explain.