The prolific and versatile historian Walter Nugent of Notre Dame University has just published a lucid, vivid, and above all candid history of American expansion under a perceptive title, “Habits of Empire” (Alfred A. Knopf, 387 pages, $30). Mr. Nugent’s account emphasizes the nation’s early years, when Americans were forming their “habits,” but his readers will undoubtedly be continually applying what he says about Franklin, Jefferson, Madison, Polk, and McKinley to what they read in their newspapers.

When I was in college in the 1950s, our teachers never used the words “empire” and “imperialism” to refer to American westward expansion. “Imperialism,” we were told, had to do with the acquisition of noncontiguous lands, not adjacent ones. Yes, America had gone through an imperialist phase, but it had been a brief aberration, cropping up after the victory in the Spanish-American War of 1898, when we took over the Philippines, Hawaii, and Puerto Rico. Mr. Nugent, by contrast, sees imperialist aspirations as a continuous thread running throughout American history from the 17th century to today.

Mr. Nugent appropriately divides the history of American imperialism into three phases: Empire I, expansion across the North American continent, 1783-1853; Empire II, the acquisition of possessions around the Pacific and Caribbean, starting with Alaska in 1867; and Empire III, America’s post-World War II global empire, an amalgam of economic power and cultural influence with military bases and alliances. He devotes most of his space to Empire I, a couple of chapters to Empire II, and a postscript of a dozen pages to Empire III. While many readers may wish for more on the recent period, Mr. Nugent’s sense of proportion is in keeping with his announced intention to write about the habits of empire and therefore to concentrate on their early formation.

In his own way, Mr. Nugent concurs with Frederick Jackson Turner’s classic thesis, “The Significance of the Frontier in American History.” But where Turner emphasized the role the frontier played as a laboratory of democracy, Mr. Nugent declares that the frontier accustomed Americans simultaneously to empire-building. On the frontier, Americans conceived and implemented big plans, brushed aside outnumbered and divided native inhabitants with the aid of superior technology, and glorified their accomplishment as the spread of civilization. They saw themselves as carrying out a mission to bring America’s enlightened institutions to the rest of the world. This habit of mind, tinged with religious providentialism and racist presumption, fed upon a mostly successful experience of expansion across North America.

My favorite chapters in the book were those that dealt with Canada and Florida, respectively. America acquired the former Spanish colonies of West and East Florida piecemeal, starting with what is now the Louisiana panhandle east of New Orleans in 1810, and gradually moving along the Gulf Coast, taking what is now the area around Biloxi, Miss., in 1811 and Mobile, Ala., in 1813. Peninsular Florida, then called East Florida, was acquired by treaty in 1819 following its invasion by Andrew Jackson in 1818. In each of these cases, incursions by private American freebooters (then called “filibusters”) into Spanish territory played a significant role, while the American government preserved public deniability of the freebooters’ activities. The fascinating stories of these events are not at all well known, even among historians.

Mr. Nugent’s chapter on Canada offers the country’s imperial experiences there as the exception to the rule of America’s successful expansion. Twice American forces invaded Canada, early in the Revolutionary War and again early in the War of 1812. Both times, the Americans expected to be welcomed as liberators; both times they instead encountered stout resistance and had to retreat. Though forgotten today by Americans, the memory of these failed invasions is preserved north of the border and taught to Canadian schoolchildren as the military confirmation of their own sense of national identity.

Americans’ ignorance of their war with Mexico, whose momentous consequences included the acquisition of California, Texas, and everything in between, is nothing short of a case of national amnesia. Mr. Nugent’s chapter on the Mexican-American War is remarkable for two features: his use of Mexican sources and his account of the inside story of how the peace treaty came about. A disobedient diplomat named Nicholas Trist, defying an order to stop negotiating and come home, instead signed a treaty of peace that transferred less Mexican territory than President Polk wanted. (Polk had intended to take Baja and everything north of Tampico, as well as the right to construct a canal through the Isthmus of Tehuantepec.) But once a courier arrived in Washington bearing the text of Trist’s treaty, Polk recognized that if he refused to submit it to the Senate for ratification, his Congressional opposition, the Whig party, would be strong enough to frustrate further prosecution of the war.

Only small criticisms of Mr. Nugent’s new book seem worth making, valuable as it to historians and general readers alike. The most significant deficit of “Habits of Empire” is that the book pays too little attention to the perennial opposition to American imperialism. However common, imperialism has been consistently controversial throughout American history, and objections have been raised to the imperial impulse from all corners of the American political stage. It would be interesting to know why, for example, the Democratic party, which enthusiastically supported Empire I under Jefferson, Jackson, and Polk, largely opposed Empire II. Republicans often opposed the early stages of Empire III, but Eisenhower successfully brought the party around to repudiate isolationism.

Whether and when the consequences of American imperialism have been good or bad for America or the world as a whole may be as much a question for political philosophy as for history. But until we face up to the historical facts, so well illuminated in this candid account, we will not be in a good position to judge.

Mr. Howe is Rhodes Professor of American History Emeritus, Oxford University, and Professor of History Emeritus, University of California, Los Angeles. He is the author of, among other books, “What Hath God Wrought: 1815-1848,” which won the Pulitzer Prize for history this year.