Niall Ferguson (prof of financial history at New York University) writes a lengthy piece in The Chronicle of Higher Education about America as an empire. (It is an excerpt from a forthcoming book.) It is interesting enough of a read (the use of the British Empire by way of comparison is helpful) even if you don’t subscribe to his thesis. I don’t think America is an empire unless, and it’s a big unless, you consider it an "empire of liberty," as Jefferson did. But that is a different, and a longer argument. Still, worth a look.
Speaking of empire, you might want to glance at this piece on a famous scholar on things African and why he decided to leave African studies: he found it too depressing. And you might even want to read Doris Lessing on what used to be called the "jewel of Africa," and what Mugabe has done to it. It is depressing.
And, finally, this Boston Globe article asks why so many of the "pro-American imperialists" commentators are not born in America, e.g., DSouza, Boot, Steyn, Johnson. This is an interesting question that this article doesnt do justice to, but its a start.