United We Stand. Since September 11 the slogan is everywhere: on the freeway into Manhattan from JFK airport, against a billboard image of the billowing stars and stripes, emblazoned on the giant trucks that rumble from coast to coast, stuck on bumpers in the Midwest ...
When entering New York after the destruction of the twin towers, the sentiment was moving. Yet, though the words remain a statement of American resolve, the assertion rings false.
However strong the common purpose against rogue Islamic groups, the US is gradually fragmenting. On a recent road-trip from San Francisco to New York, I was struck most by the observation that Americans are evolving away from each other.
I've led a sheltered existence in the US. In five years of living and travelling here, I clung to the coasts. My experiences of middle America - Wisconsin, Nebraska, Iowa, Wyoming and the other flyover states - was from a safe distance of 35,000 feet. I would look down at the area labelled the Great American Desert in the 19th century, and check how many hours were left until San Francisco.
Acquaintances bombarded me with helpful advice when I set out, recommending the shortest way across the cold and the barren. Go the southerly route: Santa Fe is great, and from there you just have to cross northern Texas, Oklahoma and Arkansas before you get to Tennessee and civilisation. Well, if not civilisation, at least Elvis.
I knew from the movies and the newspapers that middle America would be different. The inhabitants: redneck cops, slow hillbillies, desperate small-town intellectuals - cheap but funny stereotypes. The places: Waco, Laramie, Columbine - datelines from the latest massacre.
To try to delve beneath the cliche, I'd read the occasional anthropological study in the New York Times on the strange culture of the heartland. An evergreen topic refreshed by the latest Christian rock phenomenon, or a novel such as The Bridges of Madison County that emerged out of nowhere - ie, middle America - to dominate the bestseller list.
And from close up? The high production values of an anti-abortion ad on Christian radio; a fragment from the right-wing talk radio show (we're a fat and happy country being gutted by the wolves, the immigrants); Christian graffiti - 'Trust Jesus' - in Virginia; ordering a 'lady's steak' and having to split it between two of us.
During the November 2000 election, America's differences were displayed in a tidily shaded map: Pacific and East Coast states a solid Gore blue, bracketing the Bush red of middle America. More detailed county-by-county maps showed the blue liberals as a fringe around the coasts, being pushed into urban enclaves and the sea by the real America. Of course George W Bush was indifferent to global warming: a rise in sea levels would largely inundate the America that voted for his opponents.
The divide between liberal coasts and conservative heartland is more obvious now that other political issues have disappeared. There's broad consensus over economic and foreign policy. The strange alliance between Northern liberals and Southern segregationists has expired. All that is left, as a character says on The West Wing, is one corporate party with a pro-abortion and an anti-abortion faction.
And the homogeneity of the US strikes a visitor. Driving along the US interstate highway system is like the movie Groundhog Day, in which the hero is condemned to repeat endlessly a strip of Walmart, McDonald's and Home Depot.
As the South develops and northerners move in, cities such as Atlanta are becoming more liberal. The last census showed Latinos and other minorities making their way into white areas. Intermarriage runs as high as 50%.
The US has always catered to cultural defectors from the mainstream: the rich in their gated communities; pensioners in southern Florida condos; gays in San Francisco's Castro neighbourhood; northern European protestant sects in rural Pennsylvania. But Americans are evolving apart. Now entire regions, not just enclaves, are going their own way. Cities have specialised.
Entertainment in LA, technology in San Francisco and Silicon Valley, publishing and finance in New York, each attracting a certain type. With people so easily able to rent a U-Haul truck, a new apartment, and trek across the country, it doesn't take long for like spirits to collect in these city-states.
I am moving from San Francisco to New York in part because I want to be witty without being thought rude. Even the goys there behave Jewish; West Coast Jews, as one LA screenwriter observes, have become blond and bland within two generations, as if sand got into their DNA. Inhabitants of Silicon Valley are smart, earnest and awkward. Los Angelinos do indeed take more care over their appearance. Southerners are loud and friendly.
And, yes, middle Americans are fatter; the stereotype is true.