Is it possible, by constitutional arrangements, to reduce the likelihood that a nation will go to war? This is the question to which Scott Silverstone addresses this informative and carefully argued book.

The author begins by reviewing the theoretical literature (realists versus democratic idealists, Kenneth Waltz versus Bruce Russett). Such introductory material is often turgid, sometimes irritatingly so, but Silverstone accomplishes this part of his task efficiently. He argues that neither side pays adequate attention to “the most important institutional feature [in the American system] shaping domestic competition over questions of war and peace” (p. 10), namely, the provisions that ensure that a diversity of regional perspectives will come to bear on questions of national security. Some theorists, he notes, argue that democracies tend to be less bellicose than other types of regime. However, such theorists give scant attention to the varying ways in which democratic impulses are registered and channeled. Theorists who do take institutional arrangements seriously tend to look at checks and balances and the separation of powers. They virtually ignore the feature that was central to the men of 1787 about how to restrain the impulse to war: that the United States is a federal union.

The legislature, both houses of Congress, was built upon federal principles (particularly when senators were elected by state legislatures), and so was the electoral system for the executive. The Framers, he shows, counted upon this factor—the unique federal character of the American union—more than any other to restrain the dogs of war.

The bulk of Silverstone's engagingly written book consists of case studies. It focuses on American foreign relations before the Civil War, a period in which the United States declared war twice (1812 and the Mexican War), but restrained the impulse to war on numerous other occasions. The author analyzes several of those episodes: confrontations with Great Britain and Spain between 1807 and 1815, the Oregon Crisis of 1845–46, the Mexican War, and conflicts with Cuba and Mexico in the 1850s. In each of these cases, he describes the pressures and passions that impelled the nation toward war, and he examines the countering tendencies as well. He discovers that restraint is often rooted in regions of the country where an aggressive policy seems unwise or threatening to vital interests. Often, during this first half century of the young republic's life, these perspectives, working through an institutional framework built on the American federal system, succeeded in dampening martial passions.

Silverstone's treatment is subtle and pays close attention to detail. In discussing the Mexican War, for example, he recounts the familiar story of how President Polk maneuvered the nation into war by ordering General Zachary Taylor and his army to march into disputed territory, then, when Mexico fought back, demanding that Congress recognize a state of war already existing. He shows that there was no majority in Congress for war with Mexico (Whigs opposed it solidly, and Polk's own party, the Democrats, were dubious, too). However, distracted by the threat of war over Oregon, leaders in Congress were caught unawares and did not begin to resist until the president had put facts on the ground.

Most analyses stop here. The Mexican War is understood to demonstrate that the Framers' institutional arrangements (reserving to Congress the power to declare war) did not work as intended. One man, using his powers as commander in chief, led the nation to war.

Silverstone grants that point but pursues the inquiry a step further, to show that the compound nature of the federal republic operated to restrain Polk's intention to add much more territory than eventually came from this war. Polk wanted to add Mexican territory east of the Sierra Madres, or perhaps all of Mexico, to the United States. But his plans were strenuously opposed, not only by the Whigs but also by southern Democrats, led by John C. Calhoun, who feared that Mexico would not be hospitable to slavery as practiced in the American South, and also by northern Democrats, led by Martin Van Buren, who opposed any augmentation of the slave interest. Polk was firmly convinced that the national interest would be best served by annexing as much of Mexico as possible, but regionally oriented politicians, firmly ensconced in Congress, refused to support him. They would not appropriate the money needed to accomplish the president's aims. Thus, Polk was able to bend the Constitution to expand the southern boundary of Texas, but he was frustrated in his larger territorial ambitions by political arrangements that gave power to regional politicians.

Anyone wishing to review the Framers' intent on these points, or to see how the American constitutional pattern worked in the early years of the republic, should read Silverstone's superb book. It is laudably disciplined. He does not permit himself to comment on the light his analysis might shed on current controversies.

Readers, though, may be impelled by Divided Union to take another look at the effect of institutional arrangements on national security policymaking. We have spent perhaps too much time lamenting the failure of checks and balances and the weakness of Congress, and not enough time thinking about our being a federal republic. Here at the start of the twenty-first century, as we take up our responsibilities as an imperial power, we need to pay attention to the Framers' most enduring legacy: not the separation of powers but the stubborn persistence of our federal system.

President George W. Bush may have been able to bend Congress to his will in taking the nation to war with Iraq, but he may yet be restrained by regionally oriented politicians in Congress from pursuing his grand design of a world of “democratic” regimes. Whether world peace and our national interests will be well served by these interactions within the American system remains to be seen.