The Tragedy of American Diplomacy is one of these classic and famous books that's just faintly disappointing once you actually get around to reading it. I came to it knowing that it was supposed to be the definitive critique of U.S. foreign policy that launched the whole genre of New Left historiography. I found it instead to be somewhat leaden and clumsy in its prose, and basically focused on the wrong questions.
To be sure, the core of William Appleman Williams's thesis is inarguable. The basic "tragedy" of American foreign policy, as he sees it, is that our nation proclaimed the ideals of self-determination and anti-colonialism, but then we lived to contradict them.