Buried deep within America's empty heartland lies North Dakota: remote, inhospitable, a state in crisis. But as its human inhabitants give up on the plains and move out, the original settlers are on their way back. Matthew Engel reports

Outside the town of Rugby, North Dakota, just south of the Canadian border, is the geographical centre of the North American continent: the very middle of middle America. This is not a region that easily lends itself to extremes or superlatives. But North Dakota does boast the World's Tallest Structure, the KVLY-TV tower near Blanchard, which is more than a third of a mile high. And on a hillside at New Salem, it has the World's Largest Holstein Cow - a statue, you understand. ("Enjoy the view from New Salem Sue.") And on a bluff by Interstate-94 at Jamestown is a similar statue: the World's Largest Buffalo, 26 feet high, weighing 60 tonnes, and positioned in a way that suggests it is about to dump the World's Largest Buffalo Dropping in the direction of passing humanity. This might be appropriate because something remarkable is going on in North Dakota, perhaps the least-known but most troubled state in the union.

A century and a quarter after the white man colonised the place and drove the native Americans and the buffalo to the edge of oblivion, the roles are being reversed. The Europeans are facing extinction, and the ancient inhabitants may reclaim the land. The great cinematographic story of the American west has reached its end and is being rewound. From here, the inexorable spread of white people across this land now looks less like Manifest Destiny than a failed experiment, a brief historical aberration, what the geographer Frank Popper calls "the largest, longest-running agricultural and environmental miscalculation in American history".

These are the Great Plains, the empty spaces east of the Rockies that constitute one-sixth of the American landscape (excluding Alaska). Popper and his wife Deborah have devised a plan that would transform and potentially revitalise the plains by effectively erasing what the white man has done here. It is not exactly top of the agenda in Washington right now. But in North Dakota it is at the heart of an increasingly anguished debate about the state's future.

The dream is that enough of the west could be returned to open range to create what the Poppers call a "buffalo commons" and the rancher/writer Dan O'Brien describes as "an American Serengeti": a haven for nature, a magnet for tourism, a beacon for sustainable rural progress. In a sense, it is still fantasy, but the crisis on the plains is so acute that other options are falling away. No need to ask what would happen to all the people - in North Dakota, they are already on their way out.

Since 1930 the population of the US has tripled. Uniquely, North Dakota's population has fallen: little more than 600,000, roughly equivalent to the population of Manchester and Salford, cover an area the size of England. In the 1990s alone, the US as a whole grew by 13%. North Dakota went up by 0.5%, but even that figure is an illusion. The largest city, Fargo, snuggling up to the Minnesota border, is gaining, and there is growth on the native American reservations. Just about everywhere else, humanity is in retreat.

In small and evocative towns and communities all over the state, where their great-grandfathers arrived by train and covered wagon, they are giving up and getting out: in Abercrombie, Amidon and Anamoose, Wishek, Wyndmere and Zap. Many of these towns have lost 10% of their population each decade since 1930, but in the 1990s that often accelerated to 20%. Above all, the young people are going, with regret or relief, because they have no alternative.

North Dakota is not the only state with a rural crisis. The troubles affect the whole Great Plains region - South Dakota, Montana, Nebraska. Analysts expect the plains to replace the south as the nation's poorest region very soon. Nowhere else has it as bad as North Dakota, though, to which the phrase "ground zero" was applied long before it was expropriated for use elsewhere. But perhaps the original ground zero was also here, more than a hundred years ago.

No one knows how many buffalo there were in the US before the Europeans arrived, though 60 million has been mentioned. We do know the figure for 1890, after just a few short years of crazed slaughter: about 1,000. The native Americans had always hunted the buffalo ("bison", to be zoologically accurate, "tatanka" to use the native Lakota language), but the odd arrow had no impact on their numbers.

The carnage began after the civil war when the railroads began to push west. At first, the meat was needed to feed the crews building the tracks; that was why William F Cody ("Buffalo Bill") killed 4,280 animals in 18 months in the late 1860s. There were other by-products: buffalo tongues became a popular delicacy and the hides, complete with hair, were fashionable as blankets for the carriage trade.

Still, the buffalo's numbers were hardly dented. But the industrial nations needed leather - for boots, but also to drive machinery - and so the real frenzy began. Thousands of ex-soldiers poured into the plains, shot an average of 15 buffalo a day and were paid $3 a hide. Then they collected the bones to be ground into fertiliser. And since one bone was much the same as any other, the occasional native American bone found its way into the piles, too.

At first, most of the animals in Dakota were secure, because this was native American country, protected by treaty. But then rumours started that there was gold in the Black Hills, and in 1876 one George A Custer led his men into the area. There were setbacks - rather a large one as far as Custer was concerned - but the end was nigh for both native Americans and buffalo. The treaties were forgotten.

In 1883, Dakota territory passed a law protecting the bison - but by then there were hardly any left.

The defeat of the native Americans took a little longer. Before they finally succumbed, they had their own frenzy, inspired by a medicine man called Wovoka, who persuaded them that if they performed a ritual called the Ghost Dance, the old days would be restored. The dance ended with the chant, "The buffalo are coming! The buffalo are coming!"

Actually, the horse soldiers were coming. The native Americans believed their special ghost-shirts would protect them from the guns of the Seventh Cavalry. At the battle of Wounded Knee in December 1890, their world disintegrated - apparently for ever.

With the buffalo gone and the native Americans herded on to reservations, they were replaced by migrants from Europe, who were transported by rail and given the land to plant crops, raise cattle and make a future for their families, far from the wars and tyranny and poverty of home. This was "the Great Dakota Boom". It is arguable that "the Great Dakota Bust" has been going on, with only brief interruptions, ever since.

To get a sense of modern North Dakota, you have to imagine the English countryside as it might be with hardly any incomers or tourist trade. The first ingredient is there: a failing agrarian economy. And sometimes it is possible to imagine oneself in a stretched version of England: a giant Cambridgeshire east of the Missouri, an endless Ilkley Moor to the west. But here there are no commuters ramping up house prices, no farmhouse B&Bs, no tea shoppes. A few hunters come to shoot duck and pheasant in season. But it is a six-hour drive from most of the state to Minneapolis, the nearest big city.

North Dakota is beautiful. But the beauty is of the savage and unforgiving kind that comes with a savage and unforgiving climate. Last September, the temperature was still in the 90s. By late October, icicles were hanging off the eaves. Somewhere in between, there were a couple of days that could be described as equable. Alaska aside, this is the coldest state in the union: temperatures of -30 are not uncommon, -45 not unknown. It is also the windiest, and has the most extreme variations. A Dakota winter, wrote O'Brien, is something you can look forward to only "if, as with childbirth, remodelling a house or writing a novel, you forget how bad it was the last time". "Say what you like about our climate," added another local writer, Kathleen Norris, "in Dakota we say it keeps the riffraff out."

It certainly does. To most Americans, such a place is absurdly remote: "the American outback", its "empty quarter", "the great desolation". You can fly to Europe four times from a major city for the price of a flight to Fargo (changing several times). These days, the state is probably best known for the other Fargo, the Coen brothers' film, which captures the flat bleakness of the local landscape and character, and also shows a body being fed into a garden shredder. Most unfair. In a state with a history of progressive government (capital punishment was abolished in 1915), the crime rate is extremely low - it was recently declared the US's safest state for the sixth year in a row.

That makes sense, according to Miami Herald columnist Dave Barry. "You're not going to have a lot of crime in an area with essentially the same population density as Jupiter. Even if you try to commit a robbery in North Dakota, the victim will be so happy to have human companionship that he or she will invite you home for traditional North Dakota cuisine (Pork'n'Marshmallow Jell-O Casserole Surprise)." The thesis does not entirely do justice to the full repulsiveness of most of the local food.

The people are also highly educated, which is one reason they have to get out. Jessica Thomasson, who works in the Fargo planning department, is from Park River (pop: 1,535). "All my family are there. My husband's from there. I'm a planner and he's a computer programmer. We really considered how we could get back there to live but there's nothing we can do in Park River. Of the people I was at school with, only five stayed: one's a nurse, two work for farmers and a couple work in the auto parts store."

As you travel west, farther from the pull of even a modestly sized city like Fargo, the land gets more rugged and arid, the crisis more acute. I met Duane Schatz in Elgin (pop: 1,200 when he arrived in 1965; now 679), where he publishes the Grant County News. "We have an average of three deaths a month in the paper," he says. "There are no young people. There are elderly people, and they're passing away." The evidence is on his front page, where Schatz reports the local high school American football scores. The schools have had to merge to the point where some kids travel 60 miles to get there: so Towner-Granville-Upham-Willow City play Adams-Edmore-Edinburg.

The Grant County News itself incorporates the Elgin Times, Leith Index, New Leipzig Sentinel, Raleigh Herald and Shields Enterprise. If Schatz gets his wish, finds a buyer and retires, it will probably also merge with its sister paper, the Carson Press. All these towns, placed about 10 miles apart for the convenience of the farmers and the railroads, leapt into existence in the optimism of the pioneer days, and spent the 20th century quietly dying.

Outside Schatz's cosy newsroom (perhaps the only one in the US with both a broadband internet connection and a buffalo head on the wall) are the scenes of small-town decay: the Chevy dealer next door has gone out of business; the five grocery stores are down to one. Beyond, amid the immensity of the prairie, are the grimmer indications of a ravaged countryside: abandoned farms, tumbledown barns and rusting grain elevators. And the prairie sounds are there, too: the wind in the cottonwood trees, the honking of Canada geese flying south and the haunting sound of the American railroad, the hoo-woo! clank-clank-clank! of an endless freight train.

The railroads! Even now, North Dakota has a phenomenal number of lines and trains passing through (though only one slow daily passenger train). The Northern Pacific, which follows Interstate-94 past the buffalo statue, arrived in the early 1870s, after the company was allotted great quantities of land to parcel out to would-be migrants. The state capital, Bismarck, was named by rail baron Jay Cooke as a ploy to attract German migrants. He also called the land "the Fertile Belt" and the "Garden of Eden".

All this was based on the Homestead Act, passed under Lincoln's presidency in 1862, offering free 160-acre parcels to anyone who agreed to farm the land for five years. To the poverty-stricken peasants of Germany and Norway, it must indeed have sounded like Eden. "I don't know of any other time in history when a benevolent government caused more suffering than with the Homestead Act," says Hiram Drache, one of the state's leading historians.

They arrived in their thousands in the 1880s, but it was never possible to make a living farming 160 acres in the Dakotas. The growing season is short; the rainfall is low and untrustworthy - and when it comes, it tends to arrive in ferocious hailstorms that destroy whole fields, or in torrential showers that scorch the crops instead of quenching their thirst. If farmers do get through to harvest time, the distance to market alone can wreck their profit margin.

A Sioux who watched a migrant turn the first sod to plough his land remarked simply, "Wrong side up", making it clear that this land was better grazed than sown. The remark passed into folklore and helped convince farmers in the west of the state to concentrate on cattle, a decision that arguably has turned out just as disastrously. There have been fat years, when the weather and the world economy cooperated to let farmers make money: two world wars, for instance, and the 1970s, when the Soviet Union needed to import huge quantities of grain. But the fat years have been the exception, and have become ever rarer. "Sometimes survival is the only blessing the terrifying angel of the Plains bestows," Norris wrote.

In the early days, before anyone discovered all this, the pioneers had to cope with the day-to-day privations of North Dakota life. In the Fargo public library, the titles of the settlers' memoirs tell their own story: Against The Wind, The Cruel Cold Land, Summer's Past, Winter's Coming. The railroad publicity material did not mention the temperatures of 45 below, the isolation, the hardships. But once the migrants were here, they could not afford to go back. Instead, they became enlisted in the Garden of Eden conspiracy and wrote jolly letters to relatives to persuade them to come out and provide them with cheap labour.

Many went bust; some must have gone mad. Later waves of migrants were given four times as much land, and even then it was hard to make a living. The weak gave up, and the strong bought them out. With mechanisation, farmers no longer needed European dupes to do the work and a couple could look after thousands of acres with maybe an extra pair of hands at harvest time. It was a form of natural selection, of the sort that once made the buffalo supreme.

And it has taken all this time for the white man even to begin to understand what the native Americans knew instinctively, that there is a natural rhythm to life on the plains and the buffalo is beautifully adapted to it. O'Brien was one of the first, in the 1990s, to grasp that it made more sense to have bison on his land than cows. "Cattle may be fine for fertile farms that have been tamed for centuries, but on the Great Plains they always seem slightly lost, and clumsy, like someone picking their way through a pasture wearing stiletto heels," he wrote in his lovely book, Buffalo For The Broken Heart. "They have always been a sort of ungulate tourist, and in ranching them I felt like a tour guide who spends his life translating menus and pointing out the rest rooms."

O'Brien put this in scientific terms, too: cattle cower from the weather, whereas buffalo relish it; buffalo eat prairie weeds, cattle nibble the best grasses; cattle trample the ground under trees and near ponds, buffalo have a knack of seeking out the tiniest drops of water from the earth. O'Brien said his land and wildlife regenerated within a year of his switching.

And, as the old railroad crews discovered, buffalo also produce tasty meat with little fat, and without the growth hormone jabs that are the norm in American cattle-breeding. So dozens of farmers in the Dakotas strengthened their fences and changed to farming buffalo in the late 1990s. The price of breeding bulls rocketed to $3,000. And everyone - farmers, consumers, buffalo, grasses, wild flowers - was bound to live happily ever after. Weren't they?

Well, not exactly. On the Missouri Bluffs outside the little town of Washburn are Tom and Coleen Schulz, nice people (that's the norm in North Dakota) who converted their ranch to accommodate 200 buffalo and, like O'Brien, soon realised buffalo were made for the place. "You don't have to worry about them in this climate," Tom says. "If the wind's coming from the north-west, they go on a big hill and look straight into it. They just brace themselves and lay down in the same direction, never in the sheltered area. In the fall they put on their winter hair. It's so thick, you can't get your finger through it."

And the Schulzes found the animals were not without poetry, either. "One night we went out to find them," Coleen says. "There was a full moon and their backs just shone. They just stood there and looked at us, and they had this calming effect. That's when you think it's all worth it."

Unfortunately, the light of day has tended to be harsher. Prices have plummeted and times are tough. Buffalo meat has found a niche market (with good reason, it's delicious), but it needs careful cooking or it dries out. Buffalo burgers have not caught on, because you could not trust a teenager on a fast-food restaurant pittance to get them right. Would the Schulzes make the same decision again? "Hmm," says Coleen. "At my age," says Tom, who's 61, "no."

They still relish buffalo farming. The calves are just gorgeous, like little orange lambs: they only weigh 50lbs when they're born, though they grow to 2,000. They are formidable in a stampede, of course, but so are cattle. And in repose, the adult buffalo have this soulful look: a phlegmatic, philosophical stare, as though musing on their strange history. Their beards make them seem like mutant professors. The Schulzes introduced me - from a respectful distance - to Ferdinand, their prize bull, who sires about 14 progeny a year, which is above the norm for even the most ardent professor.

Despite the economics, the signs are that Ferdinand may be winning. The 1,000 buffalo of 1890 have multiplied to 350,000 today - the billionaire Ted Turner owns about a tenth of them. And the idea of handing Ferdinand back his birthright refuses to go away. When the Poppers emerged from Rutgers University 15 years ago, they were excoriated - one local journalist, Lauren Donovan, suggested they go back to "toxic" New Jersey and stop interfering with North Dakota - and received the odd death threat.

"They're East Coast people, they're geographers, they were looking at graphs," says O'Brien. "When they came out here with their more abrupt social ways, backs went up. We're funny people out here: very conservative, very repressed. But we've also sent very radical politicians to Washington. We need time. We don't just wear our hearts on our sleeves."

Now even the state's lieutenant governor, Jack Dalrymple, a Republican and large-scale farmer whose great-grandfather planted the first crops in the Casselton area in 1875, admits: "I've never seen anything that gets people talking and thinking about things so much." The Poppers, having learned their lessons in the early days, are extremely non-prescriptive. They insist the final plan could involve lots of different solutions: some commercial buffalo ranches, some conventional farms, some hi-tech industries. "It's not just buffalo that are needed," Frank says. "This is about developing land use that is somewhere between conventional agriculture and wilderness, trying to find an economic basis for the region based on restoration rather than extraction."

They do not suggest forcibly evicting anyone from their land: that was the 19th-century method. But there is already a vast acreage of public grassland from farms that failed in the 1930s. There are plenty of farmers with adjoining land who would be happy to sell if the government offered to buy them out. Thus the basis is there for a new open range, so the buffalo can roam free all over again.

The political will is not there yet, however. "The concept does not hold out," says Dalrymple the politician. "We have a lot of beef cattle in North Dakota, always have had, probably always will have. The value of buffalo has gone way down and those that have them are in trouble. This is the harsh reality of the food business. You can have all the ideas you want, but somebody has to buy it." Newspaperman Schatz, another old-school North Dakotan, is terser: "The idea's a load of baloney," he says.

Dalrymple's "always" is actually a blink of the eye in historical terms. Conventional agriculture has no serious future here, and this is a state with so few tourists that there is not even a proper guidebook. North Dakota is so desperate, it has seriously discussed removing the "North" from its name so it sounds less cold. The concept of an American Serengeti is not merely the most attractive option to revive this region, it is just about the only one.

Lauren Donovan is among those who have swapped sides. "I had this epiphany moment," she says. "It was just after my mom died and I was in this little, little town with five streets and a lot of empty buildings. I realised I was looking at something that was dying and it wasn't pretty, it wasn't quaint. It was death, and I'll never forget how sad I felt.

"When the Poppers first came here, we felt we were being attacked. But after all the anger at them, once you realise they are just the doctors delivering the bad news, all you have left is grief. I feel proud to be here and trying to carry on. But there's a lot of sadness."

There is another group of people who don't get heard very often, who are also enthusiasts for the buffalo commons. Native Americans make up about one-twentieth of North Dakota's population. Like the buffalo, their numbers are growing again from a small base, and their young people - unlike the whites - are staying: they have fewer options. But their conditions have improved a little, partly because casinos are now permitted on reservations. Thus the old starvation-poverty has diminished, to be replaced by the new American poverty, in which people get obese by gorging on huge portions of cheap, bad food. Many see the Poppers' plans as offering a new horizon.

"The buffalo commons theory fits very well with the original lifestyle and economy that was out here a century and a half ago," says David Gipp, a Hunkpapa descended from Sitting Bull's band, who is president of the United Tribes Technical College in Bismarck. "The bison was considered a sacred animal. It was part of our life and it influenced our spirituality. We have tribes who are trying to restore the buffalo herds for cultural and spiritual as well as economic reasons. This idea would mean a large part of this country would become accessible and usable to us again. Our great philosophers, such as Black Elk and Sitting Bull, talked about there being a restoration. There is a chance for a great renaissance."

Frank Popper also believes he is harking back to the most tearful passage of native American history. "The Ghost Dance craze was the dream of a defeated people that one day the buffalo would come back and their conquerors would disappear. You might say the buffalo commons is a white academic version of the Ghost Dance."

The buffalo are coming! The buffalo are coming!