Britain’s vote to quit the European Union could not have come at worse moment for a bloc that is struggling with a slew of major challenges. London’s break with Brussels will be a huge distraction for European leaders grappling with Russia’s assertiveness, the chaos in North Africa and the Middle East, terrorist attacks on their own soil and the humanitarian and political consequences of the refugee crisis.

None of these problems will go away while the terms of Brexit are hammered out. Most are likely to get worse. The EU needs not only to deal with Britain, but also to get a grip on the threats along its eastern and southern flanks. If it does not do so, it may succeed in getting a good bargain with London, only to find that it has allowed dangerous instability to grow to unmanageable levels on its periphery.