Dag Hammarskjöld, the United Nations’ second secretary-general, once offered what remains perhaps the clearest statement of the organisation’s purpose. The UN, he said, “was not created to take mankind to heaven, but to save humanity from hell”. The remark reflected the hard lessons of the first half of the 20th century, when two world wars, genocide, imperial conquest and the horrors of the Holocaust and Hiroshima devastated much of the globe. The UN was never intended to create a perfect international order; it was designed to prevent the recurrence of such catastrophes. Eighty years after its founding, that mission looks increasingly precarious. Armed conflicts are multiplying. Nuclear risks have returned to strategic calculations. International law is under pressure, while the Security Council, the world’s principal instrument of collective security, is frequently paralysed by the rival interests of its permanent members. When cooperation is most needed, faith in multilateralism is ebbing as great-power rivalry thrives. Against this backdrop, the race to succeed António Guterres, whose term ends in December 2026, has assumed unusual significance. The next …