As part of the BBC's Who Runs Your World? series, Richard N Haass, president of the US think-tank, the Council on Foreign Relations, assesses the limitations of US power and argues for deeper international collaboration.
Who runs the world? The short answer is "no one," if by "runs" one means "control".
No world government exists, and the United Nations, while many things, is anything but united. In most circumstances, the organisation lacks both the consensus as well as the capacity to impose its will on member governments or others, be they terrorist organisations or drug cartels, corporations or NGOs.
Nor does the US - by most measures the most powerful country in today's world - run things. This is, in part, because of the nature of the challenges in today's world. Terrorism, the spread of nuclear materials and weapons, global climate change - all require collective action. Talk of unipolarity and American hegemony in a global world is little more than talk.
The US cannot run the world on its own for a second reason. US strength, however great, is limited. In large part because of Iraq, the United States lacks the military means to disarm and occupy North Korea or Iran.
Similarly, the US lacks the economic means to do everything it wants given its enormous fiscal deficit and the fact that it is dependent on the continued willingness of other governments to accumulate vast holdings of dollars.
Talk of unipolarity and American hegemony in a global world is little more than talk
But none of this should be understood to suggest that we live in a state of anarchy. We do not. Contemporary international relations are not some all-out, unregulated struggle. On the contrary, there are some important principles that are widely embraced, and in some areas these principles are buttressed by institutional arrangements.
There is, for example, near-universal support for the right of self-defence, the concept that a state can respond militarily if attacked. This right is enshrined in Article 51 of the UN Charter, which explicitly states: "Nothing¿shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations."
As the text makes clear, the notion of self-defence applies not simply to the state under attack but also provides a mechanism for other parties to come to the defence of the victim.
In the realm of security, there is a host of arms control agreements that place ceilings on or eliminate entire categories of armaments, as well as so-called laws of war that influence when and how military force is to be used, including what governments are obligated to do to safeguard the rights of combatants and non-combatants alike.
There are elements of consensus in the political realm, including a number of international conventions supporting human rights and democracy and opposing torture, slavery, and genocide.
Cooperation will only materialise when the leading powers of the day determine that their self interest requires that they minimise competition with one another
Other groupings that contribute in meaningful ways to international cooperation include the G-8 (the US, Canada, France, Germany, Italy, Japan, Russia, and the UK) and many of the numerous regional organisations (the African Union, the Organisation of American States, the Association of Southeast Asian Nations, and above all the European Union) that reflect a degree of consensus about not just local but also international matters. Transatlantic arrangements, including Nato, also contribute meaningfully to political order in the world.