The writer is an honorary fellow of Trinity College, Cambridge, and author of 'Peacemaker'
The UN was created for one purpose above all others: to prevent a third world war. Eighty years later, amid multiple wars and increasingly unpredictable relations between nuclear powers, the UN needs to refocus on the all-important mission at its core.
Franklin D Roosevelt conceived of the UN as a continuation of his wartime alliance, with America and the Soviet Union working closely together, through the Security Council, to enforce a future peace. He envisioned an international air force, with bases encircling the globe, that would take on any new aggressor. Its architects believed the body would also foster an era of global co-operation, averting the economic disasters that had paved the road to war. Peace and prosperity would be mutually reinforcing.
The system never worked as intended. Cold war vetoes often paralysed the council. Yet they also staved off collapse. Unlike the League of Nations, which disintegrated when major powers walked away, the UN survived by making enforcement action against the permanent five members impossible. Survival was bought at the price of frustrating inaction.
Then, in the late 1950s, something unforeseen happened: the world began to look to the UN's leader as a peacemaker. Dag Hammarskjöld, the second secretary-general, spoke of his role as that of a "secular pope", without armies but with moral authority and an ability to talk to all warring parties. In practice, the office became crucial whenever the council stalled.
During the Cuban Missile Crisis of 1962, my grandfather, U Thant, was serving as secretary-general. His urgent, round-the-clock and now virtually forgotten diplomacy between John F Kennedy, Nikita Khrushchev and Fidel Castro crafted the pathways vital for all sides to step back from the nuclear brink.
In the late 1980s and early 1990s, secretary-general Javier Pérez de Cuéllar and his mediators negotiated settlements from Cambodia to Central America, facilitating a peaceful end to various cold war conflicts. There were terrible failures as well, for example in Rwanda, but the secretary-general's position as an honest broker was rarely questioned. Today, by contrast, the organisation is practically invisible, with a complete absence of UN peacemaking in conflict zones across the world -- from Gaza and Ukraine to the western Pacific.
When thinking about reform, attention most often turns to the Security Council. The case for updating its permanent membership, frozen from the time Soviet armies were encircling Berlin, is clear, and the inclusion of rising powers like Brazil and India would boost the body's legitimacy. But we need to remember that the UN's most valuable contributions have come not through council enforcement action, but through mediation and the unique value of the secretary-general as a neutral arbiter and diplomat of last resort.
Other global challenges, from climate change to the management of new technology, demand international co-operation. The UN can play a role in confronting these issues. But it should not pretend to be the answer to all humanity's problems.
We are creeping towards the scenario feared most by the UN founders: as memories of total war fade, armaments multiply, the logic of force replaces respect for international law and fatalism takes hold.
The existential need, the one that justified the organisation's creation, is to act as a firebreak against a catastrophic great power war. At pivotal moments in the past, from the Suez crisis in 1956 to the settlement of the Iran-Iraq war in the late 1980s, it has been the secretary-general, not the council, who has played the decisive peacemaking role.
In 2026, the world will choose a new secretary-general. The charter simply says that the General Assembly (where all 193 member states have one vote), will appoint a person on the "recommendation" of the Security Council. Usually, this has meant finding someone agreeable to the five permanent members with the rest rubber-stamping the decision.
At some point, Donald Trump, Xi Jinping and Vladimir Putin will have their say. But now is the time for everyone else to shape the selection and prepare the political backing -- including from civil society -- essential for his or her success. The wrong choice could mean the end of the only global body dedicated to peace. The right personality, a courageous and cool-headed mediator, may not only save the organisation, but could also, in the not-too-distant future, play an indispensable role in saving the world.