From the days of the Revolution the notion has taken hold, from time to time, that the United States is not so much “one nation, indivisible” as a federation of more or less distinct regions. Down to the Civil War, the nation's politics were dominated by a struggle between North and South over tariffs, slavery and control of the emergent West, and under those circumstances everybody took the importance of regions for granted. In 1889 Henry Adams devoted the first six chapters of his monumental History of America during the First Administration of Thomas Jefferson to a description of the varying social worlds of New England, the South, and the “megastates” — New York and Pennsylvania.

Thirty-six years later another influential historian, Frederick Jackson Turner, asserted in a major essay on American sectionalism that “Statesmen in the future, as in the past, will achieve their leadership by voicing the interests and ideas of the section which have shaped these leaders, and they will exert their influence nationally by making combinations between sections and accommodating their policy to the needs of such an alliance.” Some of Turner's assumptions and theories have not fared well among later historians. Some scholars have pointed out that regionalism, as an interpretative model for America, has been much subject to intellectual fashion and fads.

Whatever regionalism's merit as an ultimate explanation may be, one thing is certain: In a presidential election year there simply is no substitute for looking at the country in terms of sections. Campaign strategies are based largely on construction of regional coalitions, and of course a candidate's travel plans must reflect optimal use of time and money in each region. While Americans may ordinarily think of themselves as divided into rich or poor, Protestant, Catholic or Jewish, white or black, Mexican American or Native American, campaigns are organized primarily by region. This goes especially for the delegate selection process, increasingly — in this age of universal primaries and caucuses — an exceedingly important aspect of campaign organization.