Matthew Yglesias' book of earlier this year, Heads in the Sand, has two ambitious aims. Yglesias tries to discredit the Republican Party's foreign policy since 11 September 2001, and to argue that the Democrats' poor handling of what ought to have been an electoral advantage has meant that come an election, foreign policy and national security issues nonetheless benefit the Republicans. It is a multifacted argument, making many points persuasively. One of his critiques of some conservative thinking on foreign policy he sums up as the "Green Lantern Theory of Geopolitics". Yglesias describes this theory in terms of "the American right's valorization of willpower as the primary variable in successful war-fighting":
"In this view, there are essentially no objective limits to U.S. military might... As a premise for a foreign policy ... it leaves much to be desired. Unfortunately, since at least the wake of the Vietnam War, U.S. conservatives have tended to espouse a Green Lantern Theory of Geopolitics, believing that U.S. force can achieve essentially anything as long as the will to use it exists."
For a further elucidation of the Green Lantern Theory, Yglesias first talked about it (named, by the way, after a series of comics) in a blog post two years ago.
Even if this overstates the degree to which anyone holds to quite this formulation, this argument does get across a point about opportunity costs and setting priorities that those who advocate American global leadership cannot ignore. Will and resolve do dictate how much, if anything, America will choose to sacrifice in order to see her interests or values defended. But objective factors must and do also play a major role. American power and influence are clearly substantial, but just as considerable are the many troublespots around the world. America lacks not so much the will to assert herself against every regime and terrorist group with contrary values and interests as the military resources.
As in all things, finite resources means trade-offs and opportunity costs, and getting involved in a certain conflict or a particular part of the world makes it much more difficult to become involved in another in the same way. There is a degree to which the fiercest supporters of American global intervention make their case as a mixture of a moral obligation and an imagining of what would happen in the worst case scenario - but divorced from any question of cost or available resources.
But it is precisely in order to concentrate American power where it matters most that such considerations must form the part of any reasoning on foreign policy, and priorities must be set. This, in turn, may mean showing less resolve in some parts of the world because, by a brutal least-worst calculation, allowing something unwelcome to happen matters less there than elsewhere.
Everyone accepts this reality to some extent, but discussion of foreign policy that ignores it - that talks of facing off one looming threat without paying lip service to the issue of finite resources, without acknowledgeing that troops in one part of the world cannot be in another - is missing something vital.