Perhaps the most recurring and paradoxical trigger of change in human society has been war. - Linda Colley

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

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.

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.