In the aftermath of the US election, the pattern of Democratic blue and Republican red on the electoral map is baffling, unless you know how to read it. Ideology does not help much. "Left" and "right" are irrelevant terms from 19th and 20th-century Europe. Geographic dichotomies--big states versus small states, interior versus coasts--merely supply questions, not answers.

The clue to the US electoral map lies in ethnography. As the historian David Hackett Fischer and the commentator Kevin Phillips (among others) have demonstrated, ideology and region are surrogates for race and ethnicity in the US. American politics is, and always has been, a struggle for power between two coalitions of tribes. Two coalitions, instead of three or four, because the US inherited the "plurality" or first-past-the-post voting system from early modern Britain. Plurality systems ensure that third-party votes are wasted and so give countries relatively stable two-party democracy.

In most periods from 1789 to the present, the US has had two dominant national parties competing to control government: Federalists vs Republicans (1790s-1810s), National Republicans vs Democratic Republicans (1810s-1830s), Whigs vs Democrats (1830s-1850s), Republicans vs Democrats (1850s-present). Despite the changing names, the underlying coalitions have been remarkably stable. In effect, there have been only two main parties in American history: the northern party and the southern party.

The core of the northern party (originally Federalists, Whigs and Republicans, and now Democrats) has been citizens of New England and the "greater New England" region settled by the descendants of colonial-era New Englanders, an enormous area which includes the great lakes, the upper prairie and the Pacific north-west. The culture of these "Yankees" originated in 17th-century English Puritanism. Its legacy remains in a distinct New England Yankee culture which values moral rectitude and social reform.

The historic rivals to the greater New England Yankees in US politics have been the coastal southerners of Virginia, South Carolina, and the Gulf coast region, which they settled from the Florida panhandle to east Texas. Royalist refugees from Cromwell's Puritan dictatorship--the so-called "Cavaliers"--created a hierarchical, traditional, aristocratic society based on a plantation economy. They have always dominated the southern party (originally Jeffersonian Republicans, then Jacksonian and Rooseveltian Democrats, and now Republicans).

On opposite sides in the English civil war, and then in the US civil war, the Yankees and Cavaliers have always been on opposite sides in US politics. For generations, the moralism of Protestants in New England, such as Cotton Mather and John Adams, has clashed with the worldly honour code of renaissance country gentlemen in the south, such as Thomas Jefferson and Robert E Lee. In New England, the politics of reform was organised around the town meeting; in the coastal south, the politics of deference and patronage was based on the courthouse gang. "Good government" is a New England idea. So is the idea of American exceptionalism, of an American mission to set an example to the world, or to save it. The ancestors of the New England Yankees emigrated to the American colonies in order to found a perfect Calvinist commonwealth. By contrast, the ancestors of the southern elite emigrated to the colonies in order to get rich quick by lording it over Indians, blacks, and poor whites. For New England, the US is--or should be--a New Jerusalem. For the south, the US is simply the successor to the British empire. The southern oligarchs, like their cousins who once ran imperial Britain, think in terms of profit, not providence.

As soon as the new federal government got started in 1789, a Yankee party, the Federalists, headed by President Washington's Secretary of the Treasury, Alexander Hamilton, began fighting with the southern party, the Republicans, headed by President Washington's Secretary of State, Thomas Jefferson. The rival New England and coastal southern elites needed electoral allies. The southerners found friends among working-class whites in the north--particularly Irish Catholics. The alliance between southern whites and northern Catholics--symbolised in 1960 by the Democrat ticket of John F Kennedy (Boston Irish) and Lyndon B Johnson (Texan Protestant)--was the basis of the southern party for 200 years. It is an alliance of convenience, not conviction. Southern white Protestants of British descent, and Irish and continental European Catholics, share little other than a common enemy: the Yankee Protestants of the northeast and midwest. While the southern oligarchy sought to undermine its Yankee rivals by teaming up with immigrant Catholics in the north, the Yankee elite has consistently championed the rights of black Americans. In part, Yankee concern for black rights was genuinely inspired by Protestant moral fervour, but it was also influenced by the same strategic principle which underlay the southern-Catholic alliance: "the enemy of my enemy is my friend." Indeed, other than their opposition to white southerners, white Massachusetts Unitarians and black Mississippi Baptists have almost nothing in common.

The history of US politics is little more than the history of these two coalitions: the southern-Catholic alliance and the Yankee-black alliance. For most of American history the southern-Catholic alliance has been predominant, controlling the national government for the greater part of 1801-1861, and again from 1933 to the present. The New England-led northern party, by contrast, controlled Washington DC only in the period between Lincoln and Hoover, 1861-1933. The historic success of the southern-Catholic alliance resulted in part from the effective disenfranchisement of black Americans until the 1960s. White supremacy united the working-class Catholics of the north (threatened by black economic and social competition) with the white population of the south (whose "way of life" was based on the subordination of blacks). For their part, the Yankees combined real or nominal support for black rights with a nasty strain of anti-Catholic nativism and anti-Irish bigotry.

Successive waves of immigration from Britain and continental Europe have modified this pattern without destroying it. Beginning in the 1840s, the main immigrant groups were the Germans and the Irish. Well-behaved hordes of Germans and Scandinavians settled alongside Yankee pioneers in midwestern states such as Kansas, Minnesota and the Dakotas. The social traditions of 19th-century Germanic immigrants meshed well with the Protestant social reform ethic of the Yankees. European Catholics, by contrast, tended to join the Irish, who controlled many big-city governments in the north and midwest, in an alliance with the white south.

German Jews were such a small minority that they tended to blend in with local populations where they settled. Most American Jews are descendants of migrants from Russia and Russian-ruled eastern Europe in the 1900s. Their political culture was deeply influenced by Marxism. During the early 20th century, Jewish labour activists concentrated in the garment industry tended to ally themselves with working-class Catholics in the labour wing of the Democratic party. But the civil rights movement united Jews with blacks and their traditional allies, greater New England Protestants and Germanic Americans, against white southerners and northern white Catholics. Today, Jews are the most loyal white ethnic group in the northern coalition, which nowadays goes by the name of the Democrats.

How did the Democrats go from being the southern party in 1900 to being the northern party in 2000? Beginning in the 1960s, as a result of the civil rights revolution, a weird realignment took place in US politics, in which the two parties switched constituencies. Democrats, historically the more racist of the two parties, took up the cause of civil rights under the leadership of Lyndon B Johnson and Hubert Humphrey. In response, white southerners left the party, becoming mostly Republican by the 1990s. Many of the leaders of the hard right in the Congressional Republican party, such as Senate Majority Leader Trent Lott, began their careers in politics as conservative Democrats.

Meanwhile, liberal Yankee and Germanic Republicans in the north and midwest and on the Pacific coast, appalled by the influx of drawling right-wing Dixiecrats into what had once been the party of Abraham Lincoln and Theodore Roosevelt, migrated into the Democratic party. One of them was Hillary Clinton, a Yankee Methodist raised as a Republican in Illinois. The descendants of progressive Lincoln and La Follette Republicans from the Germanic prairie states also tend to be liberal Democrats nowadays. The names of the midwestern leaders of the Democratic party in the House and the Senate, respectively, are echt-Teutonic patronyms: Gephardt and Daschle.Conversely, there are a growing number of Republicans--such as New York mayor Rudolph Giuliani and New York state governor George Pataki--from a once-solid constituency for the old Democratic party: Americans whose last names end in vowels.

This realignment of constituencies has given each of the two parties an identity crisis. The Republicans claim to be the party of Lincoln, although most of their present-day constituents descend from people who fought for the Confederacy--or at least supported it--and thought Lincoln was a tyrant. For their part, contemporary Democrats, based in the old Federalist, Whig and Republican strongholds of the northeast and midwest, are embarrassed by institutions such as the annual Jefferson-Jackson Day dinner, which celebrates the southern slaveholders who are the patron saints of states' rights (Jefferson) and the ethnic cleansing of the Cherokee Indians (Jackson). In 1996, the Democrat Bill Clinton won--and lost--almost exactly the same states which were won--and lost--by the Republican William McKinley in 1896. Confused? If you ignore the labels, however, the two parties are pretty much what they have always been--a southern-Catholic coalition against a Yankee-black coalition, enlarged by Germanic and Jewish Americans.

The fissures in US culture parallel those in US politics. To put the matter simply, America's elite culture is north-eastern; its popular culture is southern and western. For most of American history, American intellectual life has been dominated by elite New Englanders--for the simple reason that Puritan cultural tradition encourages book-learning, which was (and is) considered vulgar by Virginia patricians, and pretentious by Kentucky populists.

In the first half of the 20th century there was a concerted attack on the New England tradition in American literature and philosophy by a motley collection of right-wing southern literati, left-wing Jewish intellectuals, and one grumpy German-American: HL Mencken. Since the 1970s, however, the left-liberal literary intelligentsia has purged the literary canon of southern writers and thinkers from John C Calhoun to William Faulkner, most of whom are "politically incorrect" with respect to race and feminism. By default, therefore, the New England tradition has become almost the only American intellectual tradition studied in the elite universities, which treat American literature as a tale of two cities: the Boston of Emerson and the New York of Whitman and various 20th-century "New York schools." At the same time, beginning in the 1970s, faux-WASP gentility, marketed by Ralph Lauren, Calvin Klein and Martha Stewart, has become the common culture of status-seeking Americans of all regions. Sipping fine wine while perusing the New Yorker at a summer cottage on Martha's Vineyard or in the Hamptons is the daydream of social strivers from coast to coast.

While New England has conquered the tiny bastions of education and taste, the south, with a little help from the west, governs the much bigger territory of American popular culture. Although salsa and Tejano music are growing in popularity, American radio stations and music video channels are still ruled by versions of southern black music (rock, rap, jazz, R&B) and country and western (actually southern white) music. Today's mass media, like the minstrel shows and vaudeville acts of the 19th century, disseminate southern music and slang to the white working-class inhabitants of every region.

If southern music provides the cultural koine for the high school educated working-class majority in all parts of the US (and even overseas), the west provides the lifestyle symbolism. In the 1950s, "ranch-style homes" were popular even on Long Island. In the 1990s, the suburbs were menaced by mild-mannered moms and dads navigating gigantic sport utility vehicles (SUVs) which, according to television ads, are capable of climbing mesas in the desert west.

This conflation of the south and west reflects a little-known quirk of US cultural history. In the 19th century, most of the west--from the prairies to the Rockies to California--was actually settled, primarily, by pioneers from New England and the Yankee midwest, along with Germans and Scandinavians. Southern migrants got no further west than Texas and Oklahoma. Nevertheless, in Hollywood movies, westerners usually have southern accents, rather than the authentic greater New England accents. Because the south was the most rural region of the US in the early 20th century, when the movie industry got started, the "southern rube" stereotype became the western stereotype as well, on stage and screen. To compound the irony, the most violent part of America in the 19th century, as it is today, was not the west, but the south. In 1880 you were much more likely to be shot on a street in Mississippi than Nebraska.

For the past three decades, conservative politicians in the US have profited by spurning tweedy Yankee elitism for twangy country and western populism (which plays as well among northern white Catholics and Latinos as among white southerners and westerners). In the 1980s, Ronald Reagan was frequently photographed riding a horse and chopping wood on his ranch. The last Democratic president to play cowboy was Lyndon B Johnson. The liberal intellectuals made fun of him. But it is no coincidence that Johnson was the last Democratic president to win a majority of the white vote. Nor is it a coincidence that the only two Democrats to be elected president since 1964 have been two centre-right southerners posing as folksy populists: Carter and Clinton. Gore's popularity rose when he got rid of his tie and vowed to fight "for the people" in a Tennessee twang. (Even so, he lost his ancestral state, and Clinton's Arkansas as well, to a cowboy boot-wearing, ranch-owning Texan born in Connecticut: George W Bush).

What does all this mean for the policies pursued by the two coalitions? When it comes to foreign policy, the divisions between the northern party and the southern party are dramatic, enduring, and somewhat contrary to received wisdom. For two centuries, the northern party (yesterday's Republicans, today's Democrats) has been the more protectionist and isolationist of the two coalitions, while the southern party (yesterday's Democrats, today's Republicans) has traditionally supported free trade, a strong military and an assertive grand strategy.

The differences between the two coalitions in trade policy reflect the old division between the industrial north and midwest and the agrarian south and mountain west. During the period of northern hegemony, 1861-1933, high tariffs protected northern American factories from British and European competition, while forcing southern and western farmers to pay more for industrial goods. The post-1945 global trading system was inspired by the free-trade ideology of conservative southern Democrats such as Cordell Hull, Franklin Roosevelt's Secretary of State and a former Tennessee Senator--an ideology inherited by today's southern Republicans. Support for protectionism remains concentrated in the northern manufacturing states where Democrats have succeeded Republicans as the dominant party.

Partisan divisions over the military reflect much deeper cultural factors. "From the quasi-war with France [1798-1800] to the Vietnam war," writes historian David Hackett Fischer, "the two southern cultures strongly supported every American war no matter what it was about or who it was against. Southern ideas of honour and the warrior ethic combined to create regional war fevers of great intensity in 1798, 1812, 1846, 1861, 1898, 1941, 1950 and 1965." At the same time, the greater New England region has been home to the most intense opposition to American foreign wars--including the second world war. For 50 years, liberal American historians have spoken of "right-wing isolationists" but the fact is that most isolationists in the 1930s were liberals or leftists. Ironically, Roosevelt found the strongest supporters for his anti-Hitler foreign policy among racist Southern conservatives, who hated New Deal liberalism but were eager to save Britain and defeat Germany. The isolationist America First committee was a miserable failure in the south.

As the southern states have gone Republican in recent years, so has America's military, in which southern whites have always been over-represented. In November 2000, during the electoral college crisis, Democratic party operatives in the contested state of Florida tried to disqualify, on technical grounds, as many overseas ballots from US military personnel as they could, on the correct assumption that American soldiers are overwhelmingly Republican.

What explains the deeply-ingrained military ethic of southerners--and the equally intense anti-military sentiments of greater New Englanders? Again, culture is the answer. The New England Puritans frowned on violence as a way of resolving social conflicts. The southern cavalier code, however, endorsed violence when personal or national honour was being "disrespected" or "dissed." According to the sociologists Richard E Nisbet and Dov Cohen, although white southerners are no more likely than northern whites to kill strangers for money, they are much more likely to kill spouses, lovers, friends, and acquaintances who have insulted them. These differences explain why southern states have higher rates of homicide--and more executions. Most black Americans share southern culture (and the Latin American culture of honour is very similar). When murders committed by blacks and Latinos are not counted, the anthropologist Marvin Harris has observed, "America's rates of violent crime are much closer to the rates found in Japan." If southern whites were then subtracted from the murder figures, the US murder rate would be lower still.

All of this means that the talk in recent years about a supposed "resurgence of right-wing isolationism" is misleading. Many commentators have found themselves confused by the ambitious liberal interventionism of Clinton and Gore and the right-wing isolationism of Patrick Buchanan. But neither Clinton nor Buchanan are typical of their parties. Buchanan has little influence on the Republican right, which has repudiated his isolationism as well as his protectionism. Clinton, like Gore, emerged from the shrinking southern conservative wing of the Democratic party. His southern-style interventionism was supported by many Jewish liberals who want a US forward military presence capable of protecting Israel and who viewed Serbia's ethnic cleansing in the Balkans as a replay of the Holocaust. But the interventionist sentiments of Jewish liberals are not shared by other groups in the Democratic electoral base, like Yankees, Germanic Americans and blacks.

This is why Europeans and Asians who believe that the Democrats will be more "internationalist" than the Republicans are mistaken. True, liberal Yankees are more in favour of constructive engagement with international institutions and norms than their southern rivals: compare the support of Clinton and Gore for the Kyoto treaty with George W Bush's hostility to UN peacekeeping missions. But when the US uses military power--unilaterally or as part of an alliance like Nato--the fiercest opposition always comes from left-wing Democrats. Republicans may not like open-ended peace-keeping operations in the Balkans, but where US and allied security interests are clearly at stake, as in the Persian Gulf or the Taiwan Strait, they are hawks. By contrast, much of the Democratic left denounced Clinton as a war criminal during the Kosovo war. If a Republican president had led the Nato effort in the Balkans, most Democrats in Congress would probably have opposed it, just as most congressional Democrats voted against the Gulf war. Tony Blair may not like their thinking on domestic politics, but if he wants a strong Anglo-American alliance then his natural allies will be found among Anglophile Virginia Republicans, not among pacifist Democrats in Massachusetts or Oregon.

An America dominated by northern Democrats would be more likely to erect trade barriers in the name of labour standards, human rights and the environment. It would also be more likely to retreat in the face of military challenges in Asia, the middle east and Europe. George McGovern's 1972 motto--"Come home, America"--still resonates among Democrats and Green voters. Chinese generals and French Gaullists who fear globalisation and dream of a multipolar world should root for the Democrats. On the other hand, Atlanticist Europeans and pro-US Asians who want to preserve a global trading system underwritten by US military power should hope that the southern-led Republicans prevail.

The ethno-cultural bases of the northern and southern parties also explain some of the policy differences on civil rights. Democrats uniformly support racial preferences for blacks and Latinos (although not Asian-Americans), while Republicans, almost as uniformly, denounce quotas as a violation of the principle of individual rights. When the subject is rights for gays and lesbians, the positions are somewhat different: the Democrats invoke the idea that individuals, rather than groups, have rights, while Republicans under pressure from the religious right tend to oppose civil rights for homosexuals.

In the immediate future, neither tribal coalition will get its way, given the near-parity of the presidential vote and the almost-even split in Congress. Indeed, America's medium-term political fate may be in the hands of two groups of swing voters: white Catholics and non-white immigrants.

Northern white Catholics are divided in their loyalties. They are attracted by the social conservatism of the newly southernised Republican party, but Republican economic conservatism, and the anti-Catholic bigotry of some Protestant religious right leaders, has deterred many of them from following their traditional southern allies into the GOP. As a result, undecided working-class white Catholics in industrial great lakes states like Michigan and Wisconsin have become an important bloc of voters in American presidential and congressional politics.

It remains to be seen how the growing numbers of Latin American and East Asian immigrants and their descendants will influence the two big parties over the coming decades. In the 1990s, Asian-Americans tilted toward the Republicans, while Latinos were largely Democratic. But these patterns may change as the immigrants assimilate. Second and third-generation Asian-Americans, shedding Confucian social conservatism, may assimilate to the subculture of affluent, socially liberal northern Protestants and Jews, two groups whom they resemble in academic and economic success.

Mexican-Americans are by far the biggest Latino group. They tend to become more Republican as they move up the social ladder. In Texas, where there are many more third, fourth and fifth-generation Mexican-Americans than there are in California, Republicans like George W Bush have sometimes captured almost half the vote. In their social conservatism, as in their Catholic heritage, Mexican-Americans resemble Irish or Italian-Americans (the historic allies of white southerners) more than they resemble blacks (the historic victims and rivals of white southerners). What is more, the high degree of intermarriage among Latinos and white "Anglos" will soon produce a new mixed-race population in California, Texas, New Mexico, Arizona and Florida--symbolised by George W Bush's half-Latino "Spanglo" nephew, George P Bush.

In the game of tribal coalit