Today's world is dominated not by one or two or even several powers, but rather is influenced by dozens of state and nonstate actors exercising various kinds of power. A 20th century dominated first by a few states, then, during the Cold War, by two states, and finally by American preeminence at the Cold War's end, has given way to a 21st century dominated by no one. Call it nonpolar.

Three factors have brought this about. First, some states have gained power in tandem with their increased economic clout. Second, globalization has weakened the role of all states by enabling other entities to amass substantial power. And, third, American foreign policy has accelerated the relative decline of the United States vis-a-vis others. The result is a world in which power is increasingly distributed rather than concentrated.

The emergence of a nonpolar world could prove to be mostly negative, making it more difficult to generate collective responses to pressing regional and global challenges. More decision-makers make it more difficult to make decisions. Nonpolarity also increases both the number and potential severity of threats, be they rogue states, terrorist groups, or militias.

Still, if nonpolarity is inevitable, its character is not. A great deal can and should be done to shape the nonpolar world. But order will not emerge on its own. On the contrary, left to its own devices, a nonpolar world will become messier over time.

Resisting the spread of nuclear weapons and unguarded nuclear materials may be as important as any other set of undertakings. If internationally managed enriched-uranium or spent-fuel banks are established, countries could gain access to nuclear power but not come to control the material needed for bombs. Security assurances and defensive systems could be provided to states that might otherwise feel compelled to develop their own nuclear programs to counter those of their neighbors. And robust sanctions could be introduced to influence the behavior of would-be nuclear weapon states.

Combatting terrorism is also essential if the nonpolar era is not to turn into a modern Dark Age. There are many ways to weaken existing terrorist organizations by using intelligence, law-enforcement resources, and military capabilities. But this is a loser's game unless something can be done to reduce recruitment.

Parents, religious figures, and political leaders must delegitimize terrorism by shaming those who embrace it. More importantly, governments must find ways to integrate alienated young men and women into their societies, which requires greater political freedom and economic opportunity.

Trade also can be a powerful force in a nonpolar world by giving states a stake in avoiding conflict, generating greater wealth, and strengthening the foundations of domestic political order - thereby decreasing the chance of state failure as well. To this end, the scope of the World Trade Organization should be extended through the negotiation of future global arrangements that reduce subsidies and both tariff and nontariff barriers.

A similar level of effort might be needed to ensure the continued flow of investment. The goal should be to create a World Investment Organization, which, by encouraging cross-border capital flows, would minimize the risk that "investment protectionism" impedes activities that, like trade, are economically beneficial and build political bulwarks against instability. Such a World Investment Organization could encourage transparency on the part of investors, determine when national security is a legitimate reason for prohibiting or limiting investment, and establish a dispute-resolution mechanism.

More effort also will be needed to prevent state failure and deal with its consequences. The US and other developed countries should enhance their military capacities to deal with the type of threats being faced in Iraq and Afghanistan, as well as establish a pool of civilian talent to assist with basic nation-building tasks. Greater economic and military assistance to increase states' ability to meet their responsibilities to their citizens and neighbors will also be essential.

Multilateralism will be critical in a nonpolar world. To succeed, though, it must be recast to include entities other than the great powers. The United Nations Security Council and the G-8 should be reconstituted to reflect the world of today rather than the post-1945 era, and the participation of nonstate actors in multilateral organizations and processes will need to be considered.

Multilateralism may have to be less comprehensive and less formal, at least initially. Networks will be needed alongside organizations. Getting everyone to agree on everything will be difficult; instead, we should consider accords with fewer parties and narrower goals.

Trade is something of a model here, insofar as bilateral and regional accords are filling the vacuum created by the failure to conclude a global trade round. The same is true of climate change: Agreement on certain aspects of the problem (say, deforestation) or involving only some countries (the major carbon emitters, for example) may prove feasible, whereas an accord that includes every country and tries to resolve every issue may not.

Multilateralism a la carte is likely to be the new order of the day. This is less than optimal, but in a nonpolar world, what is best may well prove the enemy of the possible.