Guterres, whose term as secretary-general ends on Dec 31 this year, delivered the warning at the Methodist Central Hall in London, where representatives from 51 countries met on Jan 10, 1946, for the General Assembly’s first session.

They met in London because the UN headquarters in New York had not yet been built.

Guterres paid tribute to Britain for its decisive role in the creation of the UN and for continuing to champion it.

But he said 2025 had been a “profoundly challenging year for international cooperation and the values of the UN”.

“We see powerful forces lining up to undermine global cooperation,” he said, adding, “Despite these rough seas, we sail ahead.”

Guterres cited a new treaty on marine biological diversity as an example of continued progress.

The treaty establishes the first legal framework for the conservation and sustainable use of marine diversity in the two-thirds of oceans beyond national limits.

“These quiet victories of international cooperation – the wars prevented, the famine averted, the vital treaties secured – do not always make the headlines,” he said.

“Yet they are real. And they matter.”