I'm not sure where I read about this book, but just picked it up this a.m. and have found it hard to put down. So far it's very well written and provocative.
Each chapter focuses on individuals who have promoted American empire, from Benjamin Franklin and John Quincy Adams to William Henry Seward to Henry Cabot Lodge and John Foster Dulles. And then of course the ultimate empire proponent, Paul Wolfowitz.
Here's the only review I could easily find online, which suggests the individuals combined do not make a strong enough case -- I guess time will tell. All three of these books sound interesting: