The sky will not fall, in foreign-policy terms, if the United Kingdom votes to leave the European Union. NATO is not going anywhere, nor is the UK's seat on the UN Security Council. But if Brexit does happen, Britain will start to find itself a little lonelier, and the West a little weaker.
The idea of alliance has been having a rough time in recent months. Its loudest critic is US presidential candidate Donald Trump, who has laid into America's ties with Japan and South Korea, and called NATO obsolete. But in the campaign for Brexit, too, there has been an undercurrent of disdain for the idea that like-minded countries owe each other something, and that they should stick together.
When the Times columnist Melanie Phillips wrote on Tuesday that 'no one would willingly fight and die for Brussels', she overlooked not only that Belgium is a NATO member and Brussels hosts NATO's headquarters, but that, as historian Lawrence Freedman pointed out, Britons have indeed fought and died for Brussels before. When Britain declared war on Germany on 4 August 1914, it did so in defence of Belgian neutrality.
David Cameron's warning that Brexit could put European peace and stability at risk was derided in the UK press as melodramatic fear-mongering. But his basic point was that the EU is part of a 70-year project, built out of the rubble of the Second World War, to save Europe from the scourge of conflict. Cameron's argument would have been largely uncontroversial in most European countries, and especially in Germany and France, where the importance of post-war reconciliation and a sense of common European purpose has not been forgotten.
Brexit would not, of course, be quickly followed by European war. But it would strike a cruel, and very badly timed, blow to Western solidarity. The West - loosely defined as the democracies of Europe, North America, and a handful of allies elsewhere - is at a tricky moment in its history. Non-Western, autocratic powers, China foremost among them, are challenging the liberal international order on which Western prosperity depends. Huge movements of refugees from a war-torn Middle East are straining European entry points and providing fertile ground for the re-emergence of toxic far-right political movements. Russia is testing NATO unity, and risking a dangerous military confrontation in the process.
These problems are by no means insurmountable. The West is, in material terms, strong: it accounts for a third of global GDP, and more than half of global military spending. But what these problems all share is the need for solidarity in solving them. Europe is large enough to be able to take care of even a few million refugees, but only with a plan for spreading the financial and political burden among its member states. Vladimir Putin's threats to NATO may be primarily defensive bluster, but the more divided the Western alliance becomes, the more Russia has to work with (and while the EU is, obviously, a separate institution from NATO, its very similar membership means resentment and division built up in one forum can easily spill over to the other). The trade-offs and coordination amongst friendly countries needed to face up to these challenges will be difficult to achieve, but nonetheless crucial.
Brexit would threaten the West's collective ability to cope with these problems in a number of ways. It would be a symbolic retreat from cooperation: a decision that the UK's freedom of action is more important than the shared gains offered by a limited pooling of sovereignty. Brexit would also, by definition, remove British resources and influence from EU responses to Europe's crises, from which the UK, whether it likes it or not, cannot run away. Brexit could encourage separatists in other European countries: after Britain goes, which country will be next? Moreover, governments have limited attention spans: if Europe is dealing with a series of unhappy national divorces, it will not be dealing with much else. And this is not just bad news for Europe. As ECFR analyst Jeremy Shapiro puts it, 'a chaotic, unstable Europe would be unable (and probably unwilling) to help the US confront geopolitical challenges around the world.'
The opinion of the UK's allies is unlikely to be high on Britons' minds when they vote on Thursday. Understandably, voters have been preoccupied with subjects closer to home. But other countries - including friends to whom Britain owes its support - will be watching with interest to see if the UK decides its role in the European project has come to an end. A vote to stay, even a grudging one, would be welcome relief for an anxious West. As Barack Obama put it in his open letter to the British people: 'Now is a time for friends and allies to stick together.'