The first thing you notice as you enter Robert Crawford’s suburban Chicago office is a large, framed, movie poster of Mel Gibson – sword in hand, legs astride, tartan aflame, beneath the word Braveheart. “Now,” says Crawford, who owns one of America’s largest furniture rental firms, “can you guess my relationship with William Wallace?” His eyes are twinkling.

It is not immediately obvious to me what would bridge the centuries between Scotland’s great medieval warrior and this tartan-loving midwestern businessman. I hum and haw before admitting defeat. It is very simple, says Crawford. The scourge of Edward I’s English army married a woman named Margaret Crawford – and Robert Crawford is, needless to say, a Crawford. “We all come from the same clan,” he says. “I have always been fiercely proud of my heritage.” Then he pats me on the back: “Next time we meet I will be wearing the Crawford tartan!”

Crawford’s enthusiasm is infectious. When I ask, however, if he supports Scottish independence in its upcoming vote, he demurs. “Things have moved on since the days of Wallace,” he replies. “It would be great to have our own bonnie little Camelot but I don’t think it would be practical. How would they divide up the British army and navy?”

Few Americans know about next week’s referendum. Even fewer have an opinion. Among Scottish-Americans who are following it, a majority is opposed, according to a poll by Scotland on Sunday. There is also a vocal minority who would love to see it happen. They picture Scotland with very American eyes – as a striver for liberty against a common English foe. In their telling, Scotland is the birthplace of capitalism, thrift and honest Presbyterian toil. England, by contrast, is the cradle of entitlement welfarism.

Whether leaning yes or no, both sides have a tendency to project their US political leanings on to Scotland. Some, like Crawford, are traditional Republicans, who value the Atlantic alliance. Others, like Don Campbell, a venture capitalist, whose distant ancestor arrived in Pennsylvania in 1760, are closer to the Tea party. Its motto – “Don’t Tread on me” – is of Scottish lineage. “England likes to think of itself as a democracy,” says Campbell. “But it is basically socialist. Scotland has always been about capitalism and freedom. It can only reclaim its liberty by throwing off the English yoke.”

Gus Noble, president of the Illinois Saint Andrew Society, and his wife Aisha (with apologies to Grant Wood's "American Gothic")

I protest that Scotland’s Yes campaign is largely about defending public services from a Conservative-led government in London. Campbell sounds surprised. “The Scots invented liberty,” he says. “Where else in the world but England would the government pay for your higher education?” The answer, among other places, is Scotland (not England).

The term “Scottish-American” used to be a rarity – not as uncommon as English-American, say, which is barely used, or even Welsh-American, but nothing like as ubiquitous as those who claim Irish descent. That all began to change in the 1990s. First, there was the blockbuster hit Braveheart, which gave Americans a fierce – albeit cartoonish – awareness of the history of English oppression. Then there was the runaway success of the Outlander novels, bodice-ripping romances set in 18th-­century Scotland amid the Jacobite rebellion. Having sold millions, the Outlander series has since been turned into a hit TV drama (now recommissioned for a second season). In 1998, the US Congress passed a resolution declaring April 6 each year as Tartan Day. While it pales next to St Patrick’s day, when the Chicago River turns green with dye, the Tartan sibling has boosted awareness. The number of Scottish Highland games events held in the US has now roughly tripled since the 1970s to almost 200 a year, according to Euan Hague, a scholar at DePaul University.

Aided by the internet, there has also been a surge of interest in Scottish genealogy. The number of Americans reporting whole, or partial, Scottish ancestry rose to 27.5 million in the 2009 US community census survey. Often, self-identified Scottish-Americans may only be a quarter, or an eighth, Scottish – or even less. But they choose to emphasise that strand in their ancestry. “After the end of the cold war, it became fashionable for Americans to see themselves in ethnic, rather than ideological, terms,” says Hague. “There is something particularly romantic to American eyes about Scotland. It conjures images of rugged Highlanders in kilts fighting off the redcoats. Much of it is reinvention but that doesn’t pose a big obstacle.”

Robert Crawford gamely confirms that view. As a child he could barely understand his first-generation grandfather’s lowland Scottish brogue. But he vividly recalls a happy midwestern upbringing of bagpipes, shortbread and scones. “My mother’s side is wholly Scandinavian,” says Crawford. “Perhaps I shouldn’t say it but it isn’t as colourful as Scottish culture. We don’t pay it nearly as much attention.”

Former senator James Webb in his office in Arlington, Virginia

Scottish heritage may once have been underplayed by most Americans – or concealed within a larger north European Protestant mindset. But once you train your eye, its traces are abundant. On the long drive to Crawford’s suburban Chicago office you pass the townships of Glenview, Highland Park and Bannockburn, named after Robert the Bruce’s famous defeat of the English in 1314. Mel Gibson played an outsized role in bringing such events to America’s attention. But they were always just beneath the surface. Some people, notably James Webb, the former Democratic senator from Virginia, and possible Democratic presidential contender in 2016, believe that the US would be hard to recognise without Scottish-Americans – or, to use his classification, the Scots-Irish, whom he argues form the backbone of American values. Alex Salmond, Scotland’s first minister, and leader of the Yes campaign, bought 43 copies of Webb’s book, Born Fighting, which chronicles the history of a people who fought the English on both sides of the Atlantic. “Salmond told me he loved the book,” says Webb.

If you get a chance to escape British rule you should grab it. The Irish chose to kill the bastards. The Scottish are doing it more diplomatically

Forty per cent of the revolutionary army that defeated the British in 1781 were Scots-Irish (either directly from Scotland, or Scottish Protestants from Ulster). Today, says Webb, they are derided as rednecks, hillbillies and trailer trash. Andrew Jackson, the first truly populist US president, was Scots-Irish and gave his name to that ornery culture of nonconformism known as Jacksonian democracy. Woodrow Wilson, its 28th president, was also Scots-Irish. As many as 23 of America’s 44 presidents had Scottish ancestry. “Every line of strength in American history is a line coloured with Scottish blood,” said Wilson.

Since they are heavily concentrated in the South – and along the Appalachian and Allegheny Mountains – Scots-Irish are often unfairly depicted as racist, says Webb. They are the people Hollywood loves to hate. Disdain for rednecks is the last acceptable form of racism. “Redneck is an ethnic slur,” Webb says. “But we embrace it.”

…

Today, Scots-Irish are almost certainly the largest demographic fuelling the Tea party rebellion against Obama’s America. Webb, whose ginger hair rhymes well with his inner passion, says his kin will rebel against anyone who tries to impose their morals on them. Theirs are the martial values of the US marines with which Webb once served. With it comes a whiff of the romantic “Lost Cause” of the defeated South. “To them [Scots-Irish],” writes Webb, “joining a group and putting themselves at the mercy of someone else’s collectivist judgment makes about as much sense as letting government take their guns. And nobody is going to get their guns.”

Mac McGarvey

Webb’s office sits just across the Potomac River from Washington DC, overlooking the Iwo Jima Memorial in Arlington and next to the eponymous national cemetery, which is populated with veterans’ graves, among them that of Webb’s father. At his father’s burial in 1997, Webb recited Robert Burns while his brother played “Scotland the Brave” on the bagpipes. Webb’s bookshelves are crammed with Scots-Irish eclectica, among them The Redneck Manifesto, How the Scots Invented the Modern World, Hunter S Thompson’s Hell’s Angels, Celtic Britain, Ulster, An Illustrated Yearbook and Scottish Lore and Folklore.

In the past 30 years, grand claims have been made of Scotland’s contribution to the world – and its formative influence on America’s founding fathers. Robert W Galvin’s The Genius of a People argued that the Declaration of Arbroath in 1320 (when the Scots barons vowed to overthrow any king who accepted English suzerainty) was the intellectual godfather of the US Declaration of Independence almost 500 years later. Duncan Bruce’s The Mark of The Scots is another. But none can match the influence of Webb’s Born Fighting, which came out in 2004. “I literally got thousands of letters from people saying things like, ‘Finally I know who I am!’” he says. “This is my identity!”

To Webb, Scots-Irish are the pioneering individualists of the American frontier. Yet when I press him on what he would like to see happen on September 18, he too hesitates. “It is for Scotland to sort out,” Webb says. “I don’t think it would be appropriate for me to take a position as my ties to Scotland are ancestral and cultural and not based on current citizenship.”

I sense Webb has not yet given up his political ambitions. Calling for the break-up of Britain, which is still America’s closest ally, is not a judicious stance in US politics (both Obama and Hillary Clinton have spoken in favour of the “No” campaign). Or perhaps Webb, who was navy secretary in the Reagan administration before he switched to the Democrats, still feels the tug of the Atlantic alliance. Webb advises that I will have better luck extracting an answer from the town of Grayville, Illinois, which he describes as quintessentially Scots-Irish. It also happens to be the home of Mac McGarvey, Webb’s former adjutant in the marines, who lost an arm in Vietnam but who still served as Webb’s driver for his 2006 Senate campaign. “Having one arm was no obstacle,” says McGarvey of his days chauffeuring for Webb. “But I didn’t have the stomach for all those people in Washington.”

Mac McGarvey and family in Upper Hills, Indiana, for their annual Labor Day gathering

Grayville is just nine miles down the road from the town of Albion. To hear McGarvey tell it, they might as well be separated by Hadrian’s Wall. Grayville is overwhelmingly Scots-Irish and it bears the cultural imprints of that community. As the name suggests, Albion was founded by English settlers. “If I come home in the evening and my pick-up truck is missing, I assume someone has borrowed it and will return it later,” says McGarvey, who is sipping from a can of Bud Light in his kitchen and smoking Marlboro Lights. It is 11am. After 43 years away, McGarvey returned to his mother’s home, which is nestled in a small creek of walnut trees. “This is a trusting community. We leave our doors unlocked but that doesn’t stop me from sleeping with a loaded gun by my bed.”

Although it has a population of just 1,600, Grayville has three bars. Its mayor is also its liquor commissioner. In contrast, Albion only went “wet” last year after years of prohibition. “We drink on the front porch,” says McGarvey. “In Albion they drink on the back porch. They are very puritanical. They call us the Grayville rednecks but we all drink from the same river.”

Chowder at the Labor Day gathering

One hallmark of being Scots-Irish is military service. About a hundred men from Grayville fought in Vietnam. Dressed in jeans and T-shirt and sporting a grizzly beard and a straw hat, McGarvey is something of a local celebrity. “Everyone knows who I am,” he says. Jim Webb comes to visit every now and then. “These are his people,” says McGarvey. Another feature of the Scots-Irish is rural poverty. Grayville has plenty of that. “I was 18 before I saw my first toothbrush,” says McGarvey. “I don’t think my Dad used one in his life.”

McGarvey takes me on a drive around town to point out how much has changed. In the days of the oil boom, Grayville was an important railroad stop. When McGarvey was a child in the 1950s it was hard to find parking on the main street. Now it is literally a backwater. The train station closed. And the river that once ran through the bottom of the town meandered back on itself to become an oxbow lake. Soon, Grayville’s economy may be revived by fracking, says McGarvey. There are prospectors all around. In the meantime, it scrapes by. “I have to drive for 40 miles to Evansville, Indiana, to get a decent bottle of wine,” says McGarvey, whose years serving in the military, and then in the Department of Veterans Affairs in more urbane parts of the US, gave him a taste shared by few others in Grayville. He ended his career as an impresario at Tootsie’s Orchid Lounge in Nashville – home of country and western music, another Scots-Irish tradition.

When I ask McGarvey about what Scotland means to him, his reply surprises me. “I don’t think much about Scotland – my [Protestant] family came from Dublin,” he says. “If you get a chance to escape from British rule then you should grab it. The Irish chose to kill the bastards. The Scottish are doing it more diplomatically. Even today Ireland doesn’t have full independence.”

A member of the Kyilindi Pipes & Drums in a Labor Day parade in Grayville, Illinois

The signs of McGarvey’s Celtic heritage are all around. Every September on Labor Day, several hundred McGarveys converge from all parts of the US on Grayville to partake of the annual family “chowder” – a gathering of the clan centred on the making of a vast 300-gallon soup that includes pretty much every wild animal to hand (squirrels, raccoons and even the occasional bear). There are bagpipes, tartan and other traditions. And there is more than enough moonshine to go round. “It’s a big old family tradition,” says McGarvey.

His single arm on the wheel, McGarvey takes me up the road for lunch at his local bar, a languid neon-lit joint with pool tables, fruit machines, a jukebox and chicken wings menu. We are joined by Billy McGarvey, Mac’s son, and other members of his family, including one of three brothers, in a mini-gathering of the clan. Mac sports the standard Marine tattoo – an eagle bestride the globe and the motto, Semper Fidelis (“always loyal”). Billy’s tattoo, which covers his left bicep, intrigues me more. It shows his skin ripped open to reveal a tartan layer beneath. It is a generic tartan. “We haven’t yet discovered the McGarvey tartan,” he says.

I ask them if they had heard that Scotland is holding a referendum. Most vaguely assent. I ask which way they would vote if they could. “Yes,” say five out of five voices. “Hell, yeeeees!” Billy adds for good measure. Then he apologises in case he has offended my feelings. I assure him he has not. “We don’t have anything against the English,” Mac explains. “But you should take your liberty when you can.”

Mac and his family epitomise every Scots-Irish trait that Webb has rhapsodised: instinctively egalitarian, independent and warmly hospitable – yet always ready to fight. These are gritty people. I couldn’t help speculating what they would think of the Scots if they voted No next week. Would that make them freedom-hating? Or would they pay it little heed? “We barely notice what is happening in Chicago [Grayville’s nearest metropolis] let alone Scotland,” admits McGarvey with a chuckle.

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Much the opposite applies to Gus Noble, president of the Illinois Saint Andrew Society – the state’s oldest registered charity. Founded in 1845, Noble’s society plays host to the longest-running black-tie event in the Windy City. In November it will host its 169th annual Feast of the Haggis at the Palmer House Hilton. A soft-spoken and meticulously attired Scottish expatriate, Noble has agonised about Scotland’s choice since the referendum was set. “Though I don’t get to vote, I veer between yes and no – between the head and the heart – almost on a daily basis,” he admits.

Robert Crawford, who owns one of America’s largest furniture rental firms, poses in the Crawford tartan with his wife Winnie at their Illinois home

Noble, whose Burns recitations are as theatrical as his day-to-day demeanour is gentle, admits it would be impolitic for him to declare a preference. Many of the society’s 1,200 members – a rollcall of much of Chicago’s business establishment – would be alienated, whichever call he made, he says. The society still stands for “God Save the Queen” at its gala events but it has added the “Flower of Scotland”. It was riven down the middle recently over an innovative recipe for haggis, which cannot be imported: it included lemongrass and ginger in addition to the traditional offal and oatmeal. “There were a few outraged traditionalists,” says Noble.

The longer he lives in the US – now 23 years – the more Scottish he feels. “I used to work at the British consulate in Chicago, then I ran its Welsh Development Office,” he says. “Whenever I walked into a room people would say, ‘There’s that Scottish guy.’ No one ever said, ‘Here’s that British guy.’ After a while that influences how you see yourself.” To illustrate America’s impact on his identity, Noble quotes Burns: “Oh wad some pow’r the giftie gie us, to see oursels as others see us.”

The romance of the Scottish saltire comes from some unlikely quarters. Noble’s wife, Aisha, is African-American, born and bred on Chicago’s north side. Now expecting her first child, she describes herself as her family’s amateur genealogist. Like many African-Americans, Aisha has searched relentlessly for her family’s original roots in Africa but has yet to come up with any strong leads. Quite without asking, however, she stumbled across a Scottish one. “It was only three years after I met Gus that my grandmother decided to tell me that her grandmother was Scottish,” says Aisha. “Her name was Laura Kincaid.”

Though I don’t get to vote, I veer between yes and no – between the head and the heart – almost on a daily basis

At the various St Andrew Society events – from the Burns suppers to Tartan Day and the annual tossing of the caber – people often joke with Aisha that it must be hard for her to pull off the Scottish thing. She wears the Illinois state tartan. “You’re clearly not Scottish,” they say. Aisha is far too polite to rejoin that she might well have more Scottish lineage than some of her kilt-wearing fellow guests. “I just laugh and say that I feel at home when I visit Scotland – and I do,” she says. “In Scotland they accept me without question.” So steeped in Scotland has Aisha now become, that a Scottish-American group recently asked her to serve as an interpreter for a bunch of visiting Glaswegians. “I understand Glaswegian,” she says. “Most Americans don’t have a clue what they’re saying.” Like Gus, however, Aisha declined to say which way she would vote.

How will the US as a whole respond to next week’s referendum? That, of course, depends on the result. America’s foreign policy establishment finds the prospect of Britain’s break-up alarming but unlikely. At a time when Washington is beset by more global crises than at any time in recent memory, the very notion of Scotland separating from the UK causes puzzlement. Yet it is only since the the Yes camp edged ahead in at least one opinion poll that the US media has started to take notice. At a recent event at the Brookings Institution, Washington’s most eminent think-tank, George Robertson, the former secretary-general of Nato – and a Scot – described the prospect in almost apocalyptic terms. “The loudest cheers for the break-up of Britain would be from our adversaries and from our enemies,” he said. “For the second military power in the West to shatter this year would be cataclysmic in geopolitical terms.” His dark warning earned headlines back in the UK. But it barely merited a line in the US media.

Much like the marauding Picts whom Hadrian tried to seal off from the Roman empire, today’s Scots will only garner attention if they cause trouble. In spite of recent polls, much of the smart money is still on a No vote next week. But if today’s Scots retain anything in common with their cousins in places like Grayville, that forecast should be taken with a pinch of Caledonian salt. “The Scots are warriors and poets,” Jim Webb told me – with his trademark dash of romance. “Wherever they are in time or in geography, that has usually held true.”

Edward Luce is the FT’s chief US commentator

Photographs: Jason Andrew