That is the new book by Jonathan Last, which I liked very much. Last recently wrote “In the end, demography always wins” and you will find that view writ large in the book. He also wrote “Global demographics, not domestic policy, will control who comes and who goes.”
I am one who believes that the inability of a society to reproduce itself is per se a major problem, even if you don’t accept the most pessimistic fiscal interpretation of demographic collapse. Geopolitical influence also shall not be neglected. Here is one bit:
Low-fertility societies don’t innovate because their incentives for consumption tilt overwhelmingly toward health care. They don’t invest aggressively because, with the average age skewing higher, capital shifts to preserving and extending life and then begins drawing down. They cannot sustain social-security programs because they don’t have enough workers to pay for the retirees. They cannot project power because they lack the money to pay for defense and the military-age manpower to serve in their armed forces.
That is from Last’s WSJ essay, based on his book.