Gideon Rachman notes that the American Empire fad of 2002-2003 now seems well behind us but he's got some worries:
Some worry that a world without a dominant “imperial” power will be more dangerous. Who will ensure order? Who will keep the shipping lanes open and set the rules for the global financial system? The idea that all these things will be peacefully settled at the United Nations does not seem realistic.
I think it's worth trying to draw a few distinctions here. Most of all, the idea of the United States acting in an "imperial" manner, shouldn't be conflated with the United States acting through military force. The United States can engage in imperial, but non-military conduct. We could, for example, do our best to strangle the the economy of Cuba unless it adopts a form of government we approve of and return the property of the previous dictatorship's elite. But we can also act in a way that's military, but not imperial; stationing troops in West Germany to deter a Soviet invasion. Or we might act in response to acts of direct aggression perpetrated against the United States, as when the Taliban was working hand-in-glove with al-Qaeda and al-Qaeda was blowing up America's largest office towers and so we worked to help anti-Taliban Afghans overthrow the Taliban government.
Similarly, the idea of things being settled at the United Nations isn't the same as them being settled peacefully. One thing the United Nations can do is authorize the use of military force to eliminate a threat to world peace. Another thing the United Nations Charter does is recognize the inherent right of nations to engage in individual or collective self-defense.
The specter of imperialism raises its head pretty specifically when the United States proposes that we ought to be able to launch unilateral military strikes against countries that aren't attacking anyone else. Since the United States obviously doesn't endorse a general right of countries to engage in that sort of war-fighting (if India, say, decided to take advantage of political problems in Pakistan to invade or if Syria mounted a preventive attack on Israel's WMD facilities), we're envisioning not a world of American leadership, but a world of American domination. And that's what's not working for us.
It's worth being clear about this, because I think the general trajectory Rachman's argument takes is basically right. America will soon be experiencing a period of war-weariness where there'll be a general desire to "do less" in the world. But if one defines the alternative to the Bush/Cheney brand of imperial domination purely in terms of "doing less" then inevitably the time will come once again when it seems necessary and appropriate to "do something" and, indeed, it often is a good idea to do something. But America playing an active role in the world doesn't mean America seeking to dominate the world, and avoiding a quest for domination doesn't mean eschewing the use of military force in all circumstances — it means working through legitimate institutional mechanisms.