We have no eternal allies, and we have no perpetual enemies. Our interests are eternal and perpetual, and those interests it is our duty to follow.” Thus did Lord Palmerston, British prime minister from 1855 to 1858 and 1859 to 1865, describe his country’s foreign policy at the apogee of its global power.

Donald Trump is a Palmerstonian, as a former senior official at the US state department advised me last week. If any coherent doctrine underlies the president’s assault on the world order his own country created, that is it. But Mr Trump is no Palmerston and the early 21st century is not the middle of the 19th. Mr Trump’s narrowly transactional approach, driven by ignorance and resentment, risks disaster.

The US took a very different view in the aftermath of the second world war. The jockeying for position among mutually suspicious and nationalistic great powers had led to two shattering world wars. These had left Europe prostrate. No rationally founded idea of “interest” could justify this dire outcome. The world needed a much more enlightened vision of international relations than this one had been.