Jonathan Schwarz discusses the tendency of imperial elites to prefer being enormous fish in small ponds over being big fish in a large lake:
That's the interesting thing about the standard historical trajectory of imperial elites...at a certain point they either (1) forget the power they can wield outside their country ultimately derives from a healthy society beneath them, or (2) understand that but decide they'd rather be comparatively more powerful within a poorer society and less powerful outside.
To understand choice #2 it's useful to look at an extreme example, like Saudi Arabia. Certainly it has the natural wealth to be able to oppose Israel effectively. And you'd assume their elites want to do that, given that they're always screeching about it. But effective opposition would require Saudi society to be internally far more democratic, educated and egalitarian. So the Saudi princes have decided they'd prefer their country to be a weak, poor backwater if that's what's required for them to each own nine palaces.
The signs point to the elites of the USA being the same. Look at the way the White House talks up the need to fight the War On Terror, while simultaneously reducing their actual ability to do so: alienating allies, penny-pinching on basic equipment for the troops, making decisions so mind-explodingly stupid that even incompetence can't be the explanation, like the early decision to sack 400,000 Iraqi soldiers without pay, but allow them to keep their weapons.
(Aside: the above link, by Eliot Weinberger writing for the London Review of Books, contains the most understated yet eloquent description of the mess that is the invasion and occupation of Iraq I've yet seen.)