In 1941 Time editor Henry Luce proclaimed “the American century”. Some now see this coming to an end as a result of the nation’s economic and political decline. Many point to the example of US failure to convince its allies to stay out of the Asian Infrastructure Investment Bank, Beijing’s rival to the World Bank; but this was more an example of a faulty decision than evidence of decline, which raises the question of what is the natural life cycle of a nation.

A century is generally the limit for a human organism but countries are social constructs. Rome did not collapse until more than three centuries after it reached its apogee of power in 117AD. After American independence in 1776 Horace Walpole, the British politician, lamented that his nation had been reduced to the level of Sardinia, just as Britain was about to enter the industrial revolution that powered its second century as a global power.

Any effort at assessing American power in the coming decades should take into account how many earlier efforts have been wide of the mark. It is chastening to remember how wildly exaggerated US estimates of Soviet power in the 1970s and of Japanese power in the 1980s were. Today some see the Chinese as 10ft tall and proclaim this “the Chinese century”.