Recent scholarship regarding the idea of a U.S. Empire has raised serious questions as to the feasibility and desirability of imperial ambitions. This paper traces the debate over the net-benefit of empire back to the Classical economists. Adam Smith argued that the British Empire was a net cost while John Stuart Mill concluded the same empire was a net benefit. Contemporary arguments about a U.S. Empire map neatly to the divergent views of Smith and Mill. In addition to engaging in an exercise in history of thought, we use Smith’s political economy as a means of adjudicating between the different claims regarding the feasibility of empire. In doing so, we subject the claims of proponents of American Empire against the standard of robust political economy, which holds that intervention must generate desirable outcomes where less than ideal incentive and epistemic conditions hold. In doing so, we conclude that many of the claims made by proponents are fragile under less than ideal conditions.