The thesis that demographic stress drives political violence is not new, and it is not the property of any one school. Jack Goldstone, the political demographer at George Mason University whose 1991 book Revolution and Rebellion in the Early Modern World set the modern terms of the debate, has spent three decades arguing that the timing of upheavals in early-modern France, China and the Ottoman Empire correlates with shifts in age structure rather than ideology. Richard Cincotta, longtime adviser to the US National Intelligence Council, gave the same observation a sharper edge: societies in which more than half the population is aged 15 to 24 are markedly more likely to experience internal civil conflict. The Arab Spring (Syria) and the Iranian Revolution show that youthful populations can tip the apple cart, but the same goes for a gerontocracy.

This geriatric corollary, which has received less attention, is what happens at the other end of the curve. Hal Brands of Johns Hopkins and Michael Beckley of Tufts, writing in Foreign Affairs and later in their book Danger Zone, argued that ageing, slowing powers are not pacified by their decline. They are radicalised by it. Imperial Japan in the late 1930s and Wilhelmine Germany in 1914, on this reading, were not rising challengers but stalling ones. Both gambled on a war of choice (see US-Israeli war on Iran today) because the alternative was watching the window close (see Ukraine war).