For better or worse, fighting epidemics like Ebola or preventing the most harmful consequences of climate change requires solidarity and cooperation. Retreating into unilateralism, ultra-nationalism or the politics of identity will produce nothing but a bitter, fragmented, parochial and dangerous world.

Looking to 2015 and beyond, the world desperately needs brave leaders who can take the long view. In a world where power ebbs and flows, it is in everyone's interest to adhere to a fair system of rules that respect both national sovereignty and individual rights. The heads of the world's historical powers need to recognize that it is in their interest, too, to follow the rules, and to allow rising states to help write these rules. As I have often argued, the Security Council must be enlarged, and developing countries should be given greater voting rights in the Bretton Woods institutions: the IMF and the World Bank.

In exchange, the world's newest powers must begin to take on a greater share of responsibility for the global order upon which their success depends. They can no longer stand on the sidelines, denouncing the injustices of the past. Instead, they must join their peers in building the future.

We often hear talk about the shortcomings of the UN, which stands at the heart of the international system. Too seldom do we note its achievements and successes, of which there have been many. Rather than retreat from a system that has yielded exceptional results, we must use the international community's current crisis as a historic opportunity to reshape the existing order to better meet our modern challenges.

The author, former secretary-general of the United Nations, is the founding chair of the Kofi Annan Foundation and also chairs The Elders and the Africa Progress Panel. In 2001, he and the UN were jointly awarded the Nobel Prize for Peace.

Project Syndicate