Haas’s description of demographic trends can make for a sobering read. Largely thanks to shrinking fertility, by the 2060s people 65 and older will outnumber those 15 and younger. Economies around the world will slow, and welfare systems will come under great strain. But Haas, a political scientist, draws one major positive conclusion. As populations age, he argues, states will become less capable of waging war. After all, there will be fewer resources available to spend on wars and fewer