When Kofi Annan, the United Nations’ seventh secretary-general, packs up and leaves his 38th-floor Manhattan office at the end of the year, he will be feeling a complex mix of deep nostalgia, missed opportunity and profound relief.

Mr Annan, who began to fade into the background on Monday when Ban Ki-moon was formally nominated as his successor, leaves a very different UN to the one in which he rose to power as head of peacekeeping and then secretary-general in the starry-eyed nineties. Today, nations are co-operating not so much because they want to, buoyed by idealism, but because they have to, spurred on by fear. This was driven home dramatically by North Korea’s nuclear test on Monday. Meanwhile, many of the UN’s most fundamental disagreements, over the exercise of power in an era of massive inequalities, remain unresolved.