PROMISED LAND, CRUSADER STATE: The American Encounter with the World Since 1776.<i> By Walter A. McDougall</i> .<i> Houghton Mifflin: 271 pp., $26</i>

The United States has never been isolationist. From the moment the American revolution was successful, the new nation employed a foreign policy of expansion and unilateral intervention. From 1798 to 1945, American governments not only tried to secure their continental border but also intervened abroad more than 130 times, in places ranging from Mexico, Central America and the Caribbean to Europe, the Philippines and Asia.

So-called isolationism as a policy emerged only in the period between wars from 1919 to 1941, when Washington refused to supply a security guarantee to France against further German aggression. But even in this period, the U.S. was hardly isolationist; ask any Haitian, Nicaraguan or Japanese. It is the great virtue of Walter A. McDougall’s challenging book, “Promised Land, Crusader State” that he succeeds in demolishing this and other popular myths of American history.

Though willing to cooperate with other nations in the work of economic matters, the U.S. has been singularly unwilling to allow outside powers to become involved in questions of national security. This unilateral approach to American security has carried with it an implicitly absolute goal of not permitting American security to be undermined by the behavior of other powers. Americans have, therefore, never shied away from employing unilateral force either in defense of their own borders or in defense of foreign regions viewed as vital.

In this rich study of the American experience, McDougall, a Pulitzer Prize-winning historian at the University of Pennsylvania, sets out the two polar approaches that have characterized American policy throughout history. There is an America in the role of an exemplar nation, the “promised land” that Gov. John Winthrop perceived in 1630 when he implored his followers to “Consider that wee shall be as City upon a Hill, the eies of all people are uppon us.” This is the nation that John Quincy Adams described in his Fourth of July speech in 1821 as “the well-wisher to the freedom and independence of all” and “the champion and vindicator only of our own.”

But there is also the America of Woodrow Wilson, who promised to make the world safe for democracy; the America of John Foster Dulles, who promised a crusade to roll back communism; the America of Jimmy Carter, who believed that the focus of U.S. foreign policy should be to extend social justice; and the America of Anthony Lake, Bill Clinton’s onetime national security advisor, who believed it was the mission of the United States to enlarge the democratic world through free markets.

What McDougall demonstrates convincingly is that these two Americas cannot be separated. In this bible of American foreign policy, the old testament comprises Exceptionalism, Unilateralism, the American system (Monroe Doctrine) and Expansionism. The new testament is made up of Progressive Imperialism, Liberal Internationalism, Containment and Global Meliorism.

His sympathies are clearly with the Old Testament policies, but McDougall praises the doctrine of limited containment as practiced by the Truman administration and embodied in the Marshall Plan and NATO as a way “to extend the Monroe Doctrine across the Atlantic to buttress Europe’s balance of power.” Truman’s then-under secretary of State, Dean Acheson, confirmed this when he told Congress that “control of Europe by a single aggressive unfriendly power would constitute an intolerable threat to the national security of the United States.”

In essence, McDougall believes that Americans who saw this country as the promised land thought it was foolish to try to change the world, whereas “America the Crusader State held that to refrain from trying to change the world was immoral (and stupid).”

In this reading, 19th century foreign policymakers are shown to be determined to act unilaterally in both their desire to expand territory and their determination to avoid foreign entanglements. It was American unilateralism that supported then-President Andrew Jackson’s incursion into Florida in 1817 and in then-President James Polk’s desire to obtain California that brought on the Mexican War in 1846.

It was also unilateralism that allowed then-President Monroe to endorse Secretary of State John Quincy Adams’ doctrine that no foreign state should be allowed to interfere with wars of liberation then taking place in South America. Moreover, Adams was determined that he would not accept England’s offer of a “strategic partnership” in this effort to keep the Western Hemisphere free from foreign involvements. After all, was not England the traditional threat to American sovereignty?

Nonetheless, even when insisting that European nations keep their hands off the Western Hemisphere, Adams was not prepared to do anything to materially help the Latin American republics striving to throw off the colonialist yoke. If America was indeed a republic of exceptional virtue, its task should be to perfect itself, before its “empire of liberty,” in Thomas Jefferson’s words, could be extended to others.

By the early 20th century, however, that was the very empire that America believed could now be exported to all nations. Down that long Wilsonian road lay the path to the Vietnam War, which Lyndon Johnson believed could be won only by “a social revolution” designed by America.

For McDougall, morality begins at home. As we seek to define our role in the 21st century, we must pursue the national interest, which today means maintaining core alliances in Europe and Asia (the new American system) but also, in George Kennan’s words, “seek the possibilities for service to morality in our own behavior.”

The difficulty with McDougall’s rather restrictive view of American involvements abroad is his unwillingness to see our intervention in a place such as Bosnia as a furthering of the national interest--in this case, the stability of Europe--but rather to view it as meddling in the affairs of others. On the other hand, the debate on American foreign policy should center precisely on whether our involvements are meddlesome crusades or further the national interest, as we define it. But there is no doubt that when interests and morality combine, American foreign policy is likely to be most successful.

At a time when the U.S. faces no mortal threat to its existence, when its predominance seems assured well into the next century, to believe that America knows best for others remains a dangerous assumption. In this respect, Alexander Hamilton was right to remind us, “We, as well as the other inhabitants of the globe, are yet remote from the happy empire of perfect wisdom and perfect virtue.”