Never say never. Because of the global economic crisis, habits that seemed unalterable are suddenly being altered. Americans are now saving more and consuming less. Financial institutions are no longer betting the house on risky investments they do not understand. Wealthy oil-exporting countries are tightening their belts. At least some emerging markets long prone to financial accidents are behaving with uncharacteristic prudence. Everywhere, change is in the air.

Everywhere, that is, except in the way humanity responds to its most menacing threats. You know the list: climate change, nuclear proliferation, terrorism, pandemics, trade protectionism, and more. Not one can be solved, or even effectively contained, without more successful international collaboration. And that is not happening.

When was the last time you heard that a large number of countries agreed to a major international accord on a pressing issue? Not in more than a decade. The last successful multilateral trade agreement dates back to 1994, when 123 countries gathered to negotiate the creation of the World Trade Organization and agreed on a new set of rules for international trade. Since then, all other attempts to reach a global trade deal have crashed. The same is true with multilateral efforts to curb nuclear proliferation; the last significant international nonproliferation agreement was in 1995, when 185 countries agreed to extend an existing nonproliferation treaty. In the decade and a half since, multilateral initiatives have not only failed, but India, Pakistan, and North Korea have demonstrated their certain status as nuclear powers. On the environment, the Kyoto Protocol, a global deal aimed at reducing greenhouse gas emissions, has been ratified by 184 countries since it was adopted in 1997, but the United States, the world's second-largest air polluter after China, has not done so, and many of the signatories have missed their targets.

The most recent multilateral initiative successfully endorsed by a large number of countries was in 2000, when 192 nations signed the United Nations Millennium Declaration, an ambitious set of eight goals ranging from halving the world's extreme poverty to halting the spread of HIV/AIDS and providing universal primary education—all by 2015. Although some progress toward achieving these goals has been made—mostly thanks to Asia's spectacular economic performance—the failure of rich countries to fully fund these efforts, execution problems in poor countries, and the global economic downturn make the achievement of the goals by 2015 unlikely.

The pattern is clear: Since the early 1990s, the need for effective multicountry collaboration has soared, but at the same time multilateral talks have inevitably failed; deadlines have been missed; financial commitments and promises have not been honored; execution has stalled; and international collective action has fallen far short of what was offered and, more importantly, needed. These failures represent not only the perpetual lack of international consensus, but also a flawed obsession with multilateralism as the panacea for all the world's ills.

So what is to be done? To start, let's forget about trying to get the planet's nearly 200 countries to agree. We need to abandon that fool's errand in favor of a new idea: minilateralism.

By minilateralism, I mean a smarter, more targeted approach: We should bring to the table the smallest possible number of countries needed to have the largest possible impact on solving a particular problem. Think of this as minilateralism's magic number.

The magic number, of course, will vary greatly depending on the problem. Take trade, for example. The Group of Twenty (G-20), which includes both rich and poor countries from six continents, accounts for 85 percent of the world's economy. The members of the G-20 could reach a major trade deal among themselves and make it of even greater significance by allowing any other country to join if it wishes to do so. Presumably, many would. Same with climate change. There, too, the magic number is about 20: The world's 20 top polluters account for 75 percent of the planet's greenhouse gas emissions. The number for nuclear proliferation is 21—enough to include both recognized and de facto nuclear countries, and several other powers who care about them. African poverty? About a dozen, including all the major donor countries and the sub-Saharan countries most in need. As for HIV/AIDS, 19 countries account for nearly two thirds of the world's AIDS-related deaths.

Of course, countries not invited to the table will denounce this approach as undemocratic and exclusionary. But the magic number will break the world's untenable gridlock, and agreements reached by the small number of countries whose actions are needed to generate real solutions can provide the foundation on which more-inclusive deals can be subsequently built. Minilateral deals can and should be open to any other country willing to play by the rules agreed upon by the original group.

The defects of minilateralism pale in comparison with the stalemate that characterizes 21st-century multilateralism. It has become far too dangerous to continue to rely on large-scale multilateral negotiations that stopped yielding results almost two decades ago. The minilateralism of magic numbers is not a magic solution. But it's a far better bet at this point than the multilateralism of wishful thinking.