From dubbing refugees from North Africa and the Middle East “Muslim invaders” to proclaiming Hungary a Christian homeland, Hungarian prime minister Viktor Orban is prominent mainly for his brand of right-wing populist nationalism. Yet behind the vitriol that defines Orban in the Western press is a government embarked on what may end up being the biggest natalist policy experiment in modern history — an experiment that is redefining the possibilities for modern social con­servatism. Can government policies coax people to have more babies? We’re about to find out.

Demographic transition — the shift from having many children per woman to just …