In recent centuries, the greatest crises in British history have been accompanied by deep divisions among our allies, and sometimes within our own country, in the face of the sudden emergence of new dangers.

The French Revolution sparked intense debate within Britain, and required a quarter of century of rallying reluctant allies before the final victory at Waterloo. The rise of the Nazis initially produced apathy and admiration as well as hostility, and only after two years of their violent conquests did the democratic world unite to defeat them.

In our own lifetimes, by contrast, we have become used to the idea that our western values are successful and that we are as one in making sure of that success.

Since 1945, US presidents have never given up their global leadership, morally or militarily, even though they have varied in effectiveness. Nato triumphed in the Cold War and grew alongside the European Union. The West has retained the greatest centres of innovation, finance, education and culture. Our languages and computer codes have dominated the discourse of the world.