But by their very nature, nationalisms are likely to clash sooner or later. Thus May’s insistence that Britain will leave Europe’s single market puts her on a collision course with Scottish nationalists, who have a referendum mandate for saying that Scotland wants to remain in the EU – and certainly in the single market. Moreover, 21st-century nationalisms exist in a high-pressure ecosystem of 24/7 media coverage and public scrutiny that would have appalled Bismarck, Disraeli and the tsar of Russia. Even authoritarian rulers such as Putin and Xi are riding the tiger.

By far the most serious of these potential clashes is that between China and the US. In his confirmation hearing, Trump’s new secretary of state, Rex Tillerson, compared China’s programme of island-building in the South China Sea to Russia’s annexation of Crimea, and said the new administration would tell Beijing: “Your access to those islands is not going to be allowed”.

Meanwhile, in India the commander of the US Pacific command, Admiral Harry Harris, warns: “India should be concerned about the increasing Chinese influence in the region. If you believe that there is only finite influence, then whatever influence China has means that influence India does not have.” A zero-sum game, then.

Now this is partly just the familiar dance of great powers competing for influence with each other and with third parties. But the risk of an accidental naval or air confrontation somewhere in the South or East China seas is far from negligible. And then the question would become: do Trump and Xi have the wisdom, statecraft, sound advice and, not least, domestic political elbow room to step back from the brink?