Are we a superpower or not?
While some might think you are crazy, I think this is a great question and one I have often asked. The US holds fast to the following notions: individuals need good government to prosper; representative government is the best form of government; and, the US model of representative government is the best model of representative government.
If one holds these as true, then why would one not be constantly attempting to annex (through persuasion, though, not necessarily through force) other peoples? Take the Iraq War and the stated goals to bring representative government to Iraq. At the point in which we had already toppled Saddam's regime by force and we were not working with the people to institute a new government, why did we not push for annexation?
We used to do so (Philippines, Puerto Rico, Guam, etc.) The problems seemed to arise mostly not out of these territories wanting independence but out of these territories wanting statehood (they wanted to be "more American" than they were being treated).
Sure, with Iraq, the jury is out on whether or not the Iraqi people would have accepted being a territory and/or state. But, I think that they might have accepted being three territories and three states, thus the "who gets the oil revenue" would not have been, in my opinion, nearly as big of an issue.
Of course, for Americans back home, would we want six Senators and three or four Representatives from Iraq? I do not see where liberals would specifically object; and, while conservatives might object, I think that such a move would force the Federal Government to give up more control over legislation to the States.