The second amendment, passed in 1791, allowing US citizens access to arms, was manageable when most firearms were muskets that took minutes to load. - Linda Colley

Dramatic in their scope though the maritime empires once were, it is overland empires that have proved more resilient, and variations of them are still with us. The United States, Russia, China and India call themselves nation-states, but all of them are in reality products of, and marked by, different imperial enterprises; and their respective rulers on occasion still behave accordingly. Think of Donald Trump’s casual suggestion last August that the US purchase Greenland. At the time, many put this down to Trump being Trump. In fact, he was acting in conformity with many of his predecessors. US presidents proposed purchasing Greenland in the 1860s and 1940s, and American politicians did succeed in buying other vast tracts of land, Alaska, for instance, and the huge Louisiana Purchase in 1803.

Consider the terrible outbreak of plague in the 14th century known as the Black Death. Europe suffered disproportionately, losing perhaps 50 per cent of its total population. One result of this, however, was that the living standards and wages of many of those who survived seem to have improved. This, it has been suggested, led in time to a marked increase in Europeans’ food consumption and demand for consumer goods. And this rise in demand may well in turn have contributed to the increasing number of European trading voyages across the world’s oceans in the 15th, 16th and 17th centuries.

The men who dropped an atomic bomb on Hiroshima on 6 August 1945 were deploying technology that had taken decades to develop. Nonetheless, in carrying out that act, these US airmen did effect an almost immediate transformation in the nature of warfare and in attitudes towards it.