Fred Anderson and Andrew Cayton, in the Chronicle of Higher Ed (12-3-04):

[Anderson and Cayton are the authors of a new master narrative of American history. This essay is adapted from the book, The Dominion of War: Empire and Liberty in North America, 1500-2000, to be published next month by Viking.]

... The rhetoric that justified the founding of the United States made inescapable connections between empire and tyranny. Perhaps for that reason, American historians have generally approached the imperial dimension of the nation's history obliquely, treating occurrences of jingoism like the war fevers of 1812, 1846, and 1898 as unfortunate exceptions to the antimilitarist rule of republicanism. No American Napoleon conquered this continent, no jackbooted legions subdued it; the United States grew by settlement. Apart from the regrettable Indian wars, the great movement west consisted of the essentially benign inclusion of ever-larger territorial realms into democracy's dominion, freedom's sphere. Or so Americans, for the most part, believe.