LATER THIS year, the United Kingdom could disunite. In September, Scotland is due to vote on whether to become an independent nation. There is a strong chance that the Scots will vote to go it alone, breaking a political union with England that was established over three hundred years ago, through the Act of Union of 1707. The Scots number only 5.3 million of the United Kingdom’s population of 63.7 million. But Scotland accounts for a large amount of Britain’s territory and coastline—and contains several of the nation’s finest universities, castles and golf courses. Moreover, Scotland is also where Britain’s nuclear weapons are based, and the country’s (dwindling) oil supplies are almost all located in Scotland’s coastal waters.

Americans who have not noticed that the United Kingdom might be about to break up can be forgiven. Even in England, many citizens are only just waking up to the idea that the nation they are living in might go poof later this year. When the UK government led by David Cameron agreed in 2012 that a referendum on Scottish independence would be held, it was widely assumed that the result would be a foregone conclusion. And it remains true that in the scores of opinion polls that have been taken since then, not one has yet shown a majority in favor of independence. Yet, earlier this year, the polls began to narrow. Several recent snapshots of public opinion have shown the gap between the “Yes” and “No” camps to be down to three to six percentage points.

There is also a discernible gap in the energy and optimism of the two campaigns. On a brief trip to Edinburgh earlier this year, I decided to try to visit a proindependence event and a prounion meeting. The Yes campaign held three meetings in the area over the course of two days. The No camp, however, seemed to have only two events scheduled—for the entire month. The proindependence camp also has a network of eager enthusiasts, which is expected to mount an effective “get out the vote” campaign. A Scottish journalist told me that if the proindependence camp managed to narrow the gap in the polls to three points by the time of the ballot, he expected they would emerge victorious in the actual vote—simply on the basis of their superior organization. So there is now visible nervousness and squabbling among the pro-UK forces. For one thing, Cameron is starting to realize that he may be seen as the feckless prime minister who presided over the loss of Scotland—giving him a place in the history books alongside Lord North, who lost the American colonies. In that event, he would surely feel compelled to resign as prime minister the day after a referendum defeat.

HOW DID it get to this point? What are the implications for Britain and the wider Western world? Any search for the origins of the current drive for Scottish independence must start by acknowledging the obvious fact that Scotland was independent of England for much of its political history. The monarchies of the two nations were unified in 1603, and a formal political union was agreed upon in 1707 only after a significant financial crisis threatened to bankrupt Scotland. Even after the political union was consummated, Scotland provided the base for two Jacobite invasions of England in 1715 and 1745. As a result, Scottish nationalism has a rich history of battles against England from which to create a national story that might justify independence. Helpfully, the referendum has been scheduled for the year of the seven hundredth anniversary of the Battle of Bannockburn, Scotland’s most famous victory over England. (An American friend of mine who went to a Scotland-England football match was first baffled, then awed, to see Scotland supporters carrying a banner that said “Remember 1314.”)

During the nineteenth and twentieth centuries, these historic antagonisms were widely assumed to have been buried, as the English and Scots united around common enterprises—most notably the construction and management of the British Empire. The Scots played a prominent role as explorers, missionaries and imperial administrators. The threat of invasion from the Continent—first by France, then by Germany—and the experience of fighting together in the world wars also served to unite the English and Scots. In retrospect, the end of the empire after decolonization in the 1950s and 1960s probably weakened one of the central pillars of the common British identity. Moreover, the rise of the European Union provided an indirect boost to nationalism. The EU now comprises twenty-eight members. The Scots see smaller nations such as Ireland and Slovenia with an honored place at Europe’s top table, and conclude that the EU has made it viable to be a small and prosperous nation, sheltered under the European umbrella. The EU, along with NATO, is widely assumed to provide an answer to the security concerns of small European nations, although the predicament of the Baltic states may soon put that proposition to the test.

The advent of Thatcherism in Britain in 1979 provided the potent rocket fuel of resentment that is so crucial to the success of any nationalist movement. Margaret Thatcher presided over the closure or shrinkage of many of Britain’s struggling industries. Enterprises like Scotland’s steel mills, mines and shipyards were a central part of the country’s identity. Economic change probably meant that they faced a bleak future under almost any government. But mass unemployment in Scotland at the hands of a Conservative government with its political base in southern England allowed Scottish nationalists to portray their nation’s economic problems as the product of a deliberate act of class warfare by an unsympathetic, upper-class English government.

The rise of the Labour Party government in 1997—led successively by two prime ministers who grew up in Scotland, Tony Blair and Gordon Brown—seemed to hold out the promise for a renewal of the union. New Labour set up a devolved Scottish government, with considerable powers over policy areas like education and health, in a move that was intended to neutralize Scottish grievances. It didn’t. Instead, the Scottish Labour Party was itself increasingly moribund and uninspiring, with its key figures looking for careers in London and its local party notorious for machine politics. In 2011, the Scottish National Party (SNP), whose raison d’être had always been independence, defeated Labour to take control of the Scottish government in Edinburgh. At that point, the UK government felt obliged to meet the demand of the SNP for an independence referendum.

Fatefully, by this time, the government in London was once more led by a Tory prime minister who himself was something of a toff. The leaders of Thatcher’s party, with just one member of Parliament of their own in Scotland, were peculiarly ill placed to argue the case for the union in Scotland. Cameron has deliberately avoided campaigning in Scotland, tacitly acceding to the nationalists’ case that the government in Westminster lacks legitimacy in Scotland. He has also compounded long-standing problems in the relationship between England and Scotland with some serious blunders. Initially, the SNP campaigned for a third choice to be placed on the ballot—neither independence nor the status quo, but a further transfer of powers to the Scottish government in Edinburgh, while retaining Scotland within the union. Opinion polls suggested that this option, which went by the unlovely name of “devo max,” was the most popular. But Cameron balked. He refused to put it on the ballot. He apparently believed that a binary choice would allow the UK government to score a decisive victory over Scottish nationalism. This calculation, however, increasingly looks like a reckless gamble. Cameron’s second error was to fail to insist that the eight hundred thousand or so Scots residing in England should get a vote in the Scottish referendum. This deprived the strongest unionist constituency of a vote in the Scottish referendum.

CAMERON MAY rue these moves, come September. The English are still some way from imagining how their country would feel the morning after Scotland had voted for independence. But the likely reaction would be anger and incredulity. The country would immediately face some important symbolic and substantive questions. Could it still be called the United Kingdom of Great Britain and Northern Ireland if it loses part of the island of Great Britain? Would the United Kingdom have to redesign its flag, the Union Jack—which currently contains the Scottish cross of St. Andrew (the blue bit)?

Other, more substantive issues would quickly come into focus. The Irish question would be reopened, as Northern Ireland’s status within the United Kingdom began to look increasingly anomalous. (This is one reason, incidentally, why the government of Ireland quietly dreads the prospect of Scottish independence.) What would happen to the pound? Paradoxically, the SNP—in a bid to reassure voters—has said that it would like to retain the pound. Downing Street, however, has ruled out a currency union.

This is not all. What would happen to the totems of British power and international status, the permanent membership on the UN Security Council and the nuclear weapons? The UN role would probably pass straight to the continuing government in London, much as the Russian Federation inherited the Soviet Union’s Security Council membership.

Britain’s nuclear arsenal represents a more difficult issue, since the country’s Trident nuclear weapons are kept on submarines, whose home port is the Faslane base in Scotland. It would take many years and up to £20 billion to build similar basing facilities in England. So unless the English government can persuade the Scots to abandon their current plan to go nonnuclear, Britain’s deterrent would immediately come into question. This might not be a major source of regret in Washington, since some American strategists are increasingly dismayed by the proportion of Britain’s dwindling defense budget that is eaten up by maintaining a nuclear deterrent, while more useful capacities are sliced away. Nonetheless, Britain’s defense strategy would be immediately thrown into crisis by Scottish independence. In addition to the nuclear weapons, some 50 percent of the Royal Air Force’s combat aircraft would have to redeploy south of the border.

Some analysts assume that an independent Scotland would swiftly reverse its position on nuclear weapons—particularly since a decision to go nonnuclear might complicate Scotland’s effort to join NATO. One possible deal that has been mooted posits that England might agree to share the pound with Scotland in return for maintenance of the nuclear status quo. Yet such speculation may underestimate the extent to which the SNP is wedded to an antinuclear theology. The party’s campaign documents refer to Trident missiles as “an affront to basic decency.” The SNP’s position on nuclear weapons is part of a broadly left-wing approach to foreign policy that might cause surprise and irritation in the United States. For the Scottish Left, it is axiomatic that one of the malign effects of union is that Scotland has been dragged along as the United Kingdom slavishly joined in “illegal” American wars, particularly in Iraq.

Would all this matter for the broader Western alliance? One well-placed observer who argues that Scottish independence would be a calamitous blow is Lord Robertson of Port Ellen, himself a Scot and a former secretary general of NATO. In a recent speech in Washington, Lord Robertson argued, “For the second military power in the West to shatter this year would be cataclysmic in geopolitical terms.” It would, he said, “rob the West of a serious partner just when solidity and cool nerves are going to be vital. . . . The forces of darkness would simply love it.”

Lord Robertson’s argument extends well beyond the practical issues of nuclear weapons and air-force bases. The pessimists fear that the breakup of the United Kingdom would be a major blow to the confidence of a hitherto outward-looking and engaged international power. It would inevitably consume an immense amount of political energy for the government in London. If Scotland were to vote for independence this September, that would not be the end of the matter. On the contrary, it would mark the beginning of a tortuous process of divorce negotiations. The administrations in Westminster and Edinburgh have pledged to conduct any such negotiations in good faith. But divorce proceedings have a habit of getting nasty. It is certainly possible to envisage a stalemate emerging on any number of issues, from the currency to the division of the national debt to nuclear weapons. If Parliament in Westminster were unhappy with the result of independence negotiations, it would be within its rights simply to refuse to repeal the Act of Union until a more satisfactory deal were struck. The result would be an unholy constitutional mess, generating bitter feelings on both sides of the Scottish-English border.

THE VISION of Scotland breaking away from the United Kingdom would also have pan-European and even global implications. Other would-be nations—from Catalonia to Quebec and from Tibet to Chechnya—are watching the process with fascination.

The government of Spain, in particular, is deeply uncomfortable with the very process of a Scottish referendum on independence, let alone the prospect that Scotland might indeed become a sovereign nation. That is because the movement for Catalan independence is stronger than it has been for many years, and is also demanding a referendum on independence. But Catalonia accounts for a much more significant share of Spain’s population, GDP and cultural riches than Scotland represents in the United Kingdom. As a result, Scottish independence could provoke a crisis both within Spain and within the broader European Union. The Scottish Nationalists proclaim themselves to be proud pro-Europeans (unlike, they argue, the English, who are held to be narrow-minded, anti-European xenophobes) and have always assumed that an independent Scotland would either remain as a member of the EU or would swiftly gain readmittance. But there is a very real prospect that Spain would attempt to thwart a Scottish application to join the EU, in an effort to show the Catalans that independence would mean isolation within Europe.

A row over Scotland would provoke bitter arguments within an EU that is already in the grip of a profound economic and political crisis. The picture would be further complicated by the hapless Cameron’s promise that Britain will hold a separate referendum on its own membership in the EU by the end of 2017. The effects of Scottish independence on Britain’s attitude toward Europe are unpredictable. It could make the British less confident about going it alone. On the other hand, the polls suggest that the English are slightly more hostile toward the EU than the Scots, meaning that a United Kingdom without Scotland would be a little more likely to leave the European Union as well.

The British like to believe that the way in which they are allowing the Scots to vote on independence will set a global example of the civilized and democratic way in which to handle separatist and independence movements. It is certainly hard to think of many other instances of nations that would allow themselves to be broken up by democratic means. The independence referenda that Canada has allowed for Quebec represent one obvious example. The peaceful division of Czechoslovakia is another. Elsewhere, from Tibet to Chechnya to (so far) Catalonia, separatist movements tend to get short shrift from established national governments. In the modern era—from South Sudan to Eritrea to East Timor to the former Yugoslavia—new states that have broken away and established themselves as independent nations have tended to do so against a background of violence.

In the abstract, it is possible that the Scottish independence referendum could provide an inspiring example of how to handle these issues in a civilized manner. As a practical matter, it is delusional. When Russia organized the breakaway referendum in Crimea, for example, Vladimir Putin and his supporters cited the Scottish precedent as a justification for Crimean self-determination. Of course, the difference between an agreed-upon, meticulous process that takes place over years and one that was rammed through in days using force should be patently obvious. Even so, the idea that boundaries can be redrawn within Europe to accommodate national aspirations is a potentially disruptive one. (Newly assertive Hungarian nationalists might also take note.) The Scots insist that theirs is a “civic” nationalism, not an ethnic nationalism—but the distinction is likely to be lost on the likes of Putin and Viktor Orban.

Still, if it happens, for all the difficulties and irritations involved in negotiating the divorce settlement, there are few countries that are better prepared to handle the process than the United Kingdom. Decades of decolonization have given the British plenty of practice in drawing down the flag and marching away with dignity. It can be done again. For all the understandable anxieties of Lord Robertson and others, England’s self-confidence and ability to play a role in the world would survive the blow of Scotland’s separation. The British managed to absorb the loss of the American colonies, the independence of Ireland and the independence of India—and still retained a strong sense of their own identity and greatness as a nation. If it came to it, they would absorb the independence of Scotland without too much fuss.

Gideon Rachman is the chief foreign-affairs columnist at the Financial Times.

Image: Scottish Government, CC.