Will this be the century of the immigrant?

As birth rates shrink, the value of mobile, working-age people rises. "It is just that the logic of numbers cannot be bucked altogether. Unless countries can do without economic growth, employable people are going to be precious. The hunt for them will have to be passport-blind. In recent years, the nation-state has gained in power over the roving individual. That ascendancy is liable to flip." Argues Janan Ganesh.