Apparently in 2002 the Pentagon commissioned a study (which I've not read yet) of imperial power entitled the "Military Advantage in History," with a view to appreciating what the United States could learn from previous imperial adventures. Since the US is an imperial power, that's not too daft a project.
More on this later, perhaps. But for now I was struck by Dana Goldstein's response:
It's fascinating that although Roman history can be read as a cautionary anti-imperial tale, the ONA [Office of Net Assessment] report lauds Rome as the foremost example for an American empire, without even nodding toward Rome's failures or fall. But it's not too surprising that a history report written by military contractors -- not historians -- lacks complexity and was drafted to fit the pro-war preconceptions of its intended readers. One thing I hope we can look forward to under the next administration is, of course, a return of real, credentialed experts to their rightful place as government advisers.
I suppose you could see Roman history as "a cautionary anti-imperial tale" though I'm not sure what the point of doing so would be. Given that the Roman Empire* endured for 400 years it might, therefore, be considered such a success (in its own terms) as to make any comparisons with the United States - whether celebratory or condemnatory - almost entirely useless. As for "nodding toward Rome's failures or fall", this too would seem to be missing the point by an all but impossibly wide margin.
Anyway, full story on the report is in Mother Jones, here.
UPDATE: the western Empire anyway. Mr Worstall, in the comments, is right.