For diplomats and UN veterans, the swirl of this week’s General Assembly will be tinged with nostalgia. For most of the UN’s nearly eight decades, this was its high point when world leaders met to argue over the pressing causes of the day. No longer.

Despite war in Europe, a spate of coups in Africa, natural disasters blamed on climate change, and friction between China and America, this year only one leader of the “P5” — the five veto-wielding permanent members of the UN’s Security Council — plans to attend.

Joe Biden, the US president, will on Tuesday address the assembly, as have his predecessors, often memorably and sometimes combustibly over the years. But in a reflection of the impasse on the Security Council, caused by the tensions between western powers and Beijing and Moscow, the leaders of Britain, China, France and Russia are staying away.