For the people of Afghanistan the return of Taliban rule is a tragedy and a betrayal of trust. For the US the flight from Kabul is a strategic defeat. And for Europe it is a jolting description of the world as it has become.

Historians will recognise in this week’s grim events a metaphor for the geopolitical upheavals of the opening decades of the present century. When US troops arrived in Kabul after the al-Qaeda attacks of September 11, 2001, the ruling assumption was that global US pre-eminence would go unchallenged for as far as the eye could see. In truth, the post-cold war unipolar moment was already passing.

The challenge to the old order has not come solely from the great power ambitions of an emboldened China. Turning economic and military might into global power requires political will. And leadership carries a price. Defeat in Iraq, stalemate in Afghanistan and economic troubles at home have left Americans weary of paying it. President Joe Biden may have been embarrassed by the television images, but the voters wanted out.