Leading article: Nelson Mandela's greatness transcended nation and tribe

On 11 February 1990, in one of the transcendent moments of the 20th century, Nelson Mandela walked free from a jail in South Africa and gave hope to the world.

It was one of those rare events that suspend our disbelief that human nature can ever change, that some crises are not intractable, that in the end might does not always prevail. Twenty years on the world has rarely been so in need of another Mandela moment.

Some imagined that this would be the age when globalisation would conquer all. Humankind's various tribalisms, of nationalism and religion, of race and colour, would be made irrelevant on a wired-up planet where communication was instant and all-enveloping. It has not been so.

In this February of 2010, the old tribalisms appear stronger than ever, and beyond anyone's power to control. The release of Mandela, combined with the collapse of communism in eastern Europe, had seemed to signal the triumph of democracy. Today, by most accepted indices, freedom is on the retreat across the world and repression again on the advance.

The Cold War is over, but it is being replaced by mercantilist rivalries between the West, China and other emerging new powers – rivalries that economic recession has only sharpened. Their inability to look beyond their own interests was perfectly illustrated by last December's ineffectual Copenhagen conference on climate change, an overarching challenge that respects no religion, race or border.

A year ago, some saw the inauguration of Barack Obama as another Mandela moment, when an African-American at the helm of the sole superpower might solve his own country's problems but inspire the world to new and better ways. It has not been so.

Regionally too, old tribalisms are on the march. The European Union, the most ambitious and hitherto successful supra-national effort of the last half-century, faces one of its greatest trials, to prevent a collapse of the single currency that would probably deal a fatal blow to the entire European enterprise. In the Middle East, where the brew of tribes, nations and religions is more poisonous than anywhere, a new explosion threatens, centred on Iran and its nuclear ambitions.

By their nature, tribalism and nationalism find it almost impossible to see beyond the interests of the group. That leads all too often to the view that one's own group is automatically right, and the others are wrong. Nelson Mandela was different. Tribes and nations have prejudices and grudges hardwired into their systems. They cannot forgive. But Mandela could, even after almost three decades in prison.

Post-Mandela South Africa of course has not magically become a utopia where every tribalism has vanished. Yes, in four months' time the country will play host to football's World Cup, the four-yearly celebration of arguably the closest earthly equivalent to a unifying global religion. But while the black majority now rules, old racial divisions subtly persist and new ones have arisen. Crime and corruption are rife. In short, disbelief cannot be suspended. Tribalism and nationalism have driven human history, and probably they always will.

Nonetheless, humanity would perish without hope, and every so often, something happens, or someone emerges, to renew that hope – to inspire us to believe that it need not always be so, that our species can become better. This is the domain of miracles and heroes. The domain, in other words, of Nelson Mandela.