This time next year, the country known as the United Kingdom may be about to disappear.

If Scotland’s separatist government gets its way in a referendum planned for September, the 300-year-old union of Scotland, England, Wales and Northern Ireland — the United States’ oldest and closest ally — will be on the road to disintegration.

That is a dramatic, though accurate, way of describing the possible secession of Scotland from one of the world’s most successful political, social and economic unions.

The ties that bind the UK are strong, but there would be profound international implications should the Scottish people choose secession.

The residual UK would still be a major player in the world, but upon losing a third of its land mass, five million of its population and a huge amount of credibility, its global standing would inevitably diminish.

The global balance would be substantially upset should one of the West’s key unions, and its second-biggest defence power, split up.

The UK has always punched above its weight diplomatically and militarily. A breakup would have a serious effect on its role in the world — all the more so because Britain’s nuclear-deterrent base is in Scotland, and those advocating separation have pledged to expel it.

With the US and other countries viewing a possible British withdrawal from the European Union as negative, how much more disturbing would they find a breakup of the country itself?

The ripple effects would not be limited to the UK. Other separatist movements in Europe are watching the Scottish debate with undisguised interest. In Spain, more than a million Catalans have turned out in the streets calling for independence.

In the Basque Country, separatist violence has waned, but the desire for a separate state remains. In Belgium, whose unity hangs on a thread, Flemish nationalists have made it clear that if Scotland has a free pass to the European Union and Nato, they would be next in line.

The re-Balkanisation of Europe should give many pause. In a fragile, unstable world where problems and solutions are going global, going local would benefit no one. Separatism offers little by way of comfort to worried populations. It promises more strife and dissension.

Scotland’s nationalists gained control in the country’s devolved Parliament two years ago. Now they like to say that everything will change but also stay the same. This is not convincing. Secession is secession; a separate state is just that.

Consider their claim to continuity. It has been promised that Scotland would keep the same queen, the same single market and regulatory regime (this depends on the outcome of difficult and not necessarily favorable negotiations), the same currency (this presumes a euro-like currency, about which the other nations of the UK are sceptical or outright hostile) and EU membership (the decision process on whether to include a new country would be contentious).

Separatists pledge the same TV programming (but with a Scottish authority taking over from the BBC) and membership in Nato (even though their strident anti-nuclear stance would effectively bar them from a nuclear alliance).

All these assertions were spelled out in a 670-page blueprint published last month by the Scottish government. Already, it’s clear that serious questions about currency, taxation and pensions will not be answered until the breakup vote — and, indeed, cannot be until negotiations are concluded.

The proclamation that a Scotland divorced from the rest of Britain would be richer, healthier, more influential and fairer has not been substantiated.

I doubt that my fellow Scots will take the drastic blind step that secession would require. Support in the polls refuses to rise above 30 per cent. But this is no romantic “Braveheart” moment. The separatists are deadly serious, well-organised and well-funded.

Britain’s friends around the world need to pay attention. A dangerous historic event might soon be upon us — with few people outside the U.K. even noticing.

Lord George Robertson was secretary general of Nato from 1999 to 2003 and Britain’s defence secretary from 1997 to 1999.

—By arrangement with the Washington Post