KEY POINTS:
The world is increasingly having to deal with growing numbers of refugees. It may prove to be one of the greatest challenges of the century.
Almost 40 million people have been uprooted and forced to flee violence and persecution.
In the future more people will be on the move. Many of them will be in search of economic opportunity and better lives, or escaping environmental degradation and natural disasters. Others will be forced to flee failing states wracked by violence and persecution.
Sudan is a country at the epicentre of one of the world's great displacements. I have seen firsthand the dreadful suffering this means for ordinary people. And some encouraging signs of progress.
Hopes have not been fulfilled that globalisation would naturally bring steady growth while also narrowing the gap between rich and poor. While global trade and wealth have indeed increased, the gap between the world's rich and poor is widening.
It is driving more people to move and to fall prey to unscrupulous groups whose new business line in human smuggling and trafficking is worth billions of dollars a year.
Climate change and environmental damage lie behind increasingly frequent natural disasters with dramatic human consequences. Different models of the impact of climate change all present a worrying picture of human displacement.
East Africa offers a stark example. All predictions are that desertification will expand steadily, making it difficult for people to earn a living and provoking further migration. All of this is happening in the absence of an international capacity and determination to respond.
People are also fleeing war and persecution. Even when we have plenty of early warning, the international community has repeatedly failed to prevent conflicts. Instead, agencies like mine are left to deal with the human consequences.
Prevention is possible, more effective and cheaper. But it requires wisdom, political and diplomatic effort and an investment in eliminating the root causes, including the social and economic ones.
Sudan's Darfur crisis is a good example of the complexities. The conflict has political roots, but is also fuelled by increasing competition between traditional herders and farmers for scarce resources, like water.
When this is linked with political tensions, the results are explosive. The relatively recent concept of humanitarian intervention argues that states have an obligation to protect their citizens, and if they are unable or unwilling to do so, then the international community should step in.
But in the aftermath of events in Iraq, the idea of an international "responsibility to protect" is losing favour. It can be extremely difficult to help people who are displaced within their own countries and who - unlike refugees outside their homelands - are not covered under international law.
But there's good news too, as in the remote south of Sudan where tens of thousands of Sudanese refugees are making the choice to return to their devastated homeland after decades of conflict. Although largely unreported, they are coming home with UN help from refugee camps in Uganda, the Democratic Republic of the Congo, Kenya, Ethiopia and the Central African Republic.
Others are returning from exile in Libya and Egypt, as well as from other parts of Sudan itself.
Like virtually all of the world's people forced to flee violence and persecution, the southern Sudanese have long dreamed of going home - despite the uncertainties and hardship. And all of them deserve much more support than they have been getting.
I joined southern Sudanese as they returned from Uganda to begin rebuilding their lives. Our greatest satisfaction comes from helping a refugee family go home, and their repatriation is a ray of hope in a strife-torn region.
But even when conflicts are resolved and the uprooted are able to go home, their problems are not over.
Some 50 per cent of countries that emerged from conflict in recent years fell back into strife - a reminder of the imperative of addressing in a comprehensive way the complex challenges that push so many people from their homes.
It is time to recognise that we are facing what is nothing less than a new paradigm of displacement in the 21st century.
There are no easy answers, but while the international community grapples with the root causes of displacement, it must pay more attention to protecting the vulnerable and building opportunities for their futures.* Antonio Guterres, a former Prime Minister of Portugal, is the United Nations High Commissioner for Refugees.
