So Britain, which two years ago voted to leave the European Union, has now rejected the only deal on the table providing terms for that exit — and decisively so.

The outcome was largely fore-ordained, as the opposition parties had no reason to support the deal and the Conservative Party's partners, the Democratic Unionists of Northern Ireland, have stood foursquare against the deal because of its implications for the unity of the United Kingdom. The only question had been the margin, which we now know was a historic 432-202, the worst drubbing that any British government has ever received on an important measure.

Where Britain goes from here — back to Brussels in the hopes of extracting further concessions, or back to the people for a second referendum or new elections to Parliament — remains to be seen. But the rocks on which May's Brexit deal has foundered have revealed that the deeper question is whether Britain itself has a future.

The deal was rejected because it satisfied nobody. Those opposed to any exit from the EU were unhappy for obvious reasons. But those in favor of restoring British sovereignty were unsatisfied because the deal would have kept Britain tethered to the EU while a so-far elusive solution to the problem of Northern Ireland's border with the Irish Republic was resolved. That solution is likely to remain elusive now: It's impossible for Northern Ireland to have seamless relations with the Republic on matters of trade and migration without either making division between that nation and the rest of the U.K. or applying those same conditions to the U.K. as a whole. The circle cannot be squared.

That problem remains a problem, though, only inasmuch as the U.K. remains as committed to hanging on to Northern Ireland as Northern Ireland's Unionists remain committed to sticking with the U.K. And the U.K. is wobbling. When polled last year, two-thirds of Leave voters said they would chose a "hard border" in Ireland if that were the only way to get out of the EU, and fully 60 percent "would not mind either way" if Northern Ireland voted to leave the U.K. entirely. Nigel Farage isn't wrong that Brexit should be a very simple matter. It is — so long as you don't worry about holding the U.K. together after it's accomplished.

The vote for Brexit has been often described as a populist revolt by the countryside against the globalists in London — and it was that. But it was also a very distinctly English revolt. The victory margin for Leave in England and Wales was nearly double the margin in the U.K. as a whole — because Northern Ireland voted to Remain by a margin of nearly 56 percent to 44 percent, while Scotland voted a whopping 62 percent to 38 percent. And while Leave won every region of England but London, Remain won every single counting area in Scotland. If it was a nationalist reaction to globalism, it was English nationalism, not British.

If May's deal fails, her government falls, and Brexit is effectively canceled, all because of Northern Ireland, English nationalism could well become all the more truculent in the areas where it holds the greatest sway. But if Brexit does go through in some fashion, that will surely fan the flames of Scottish nationalism. Even though Scotland would have a far easier time leaving were Britain to remain in the EU (since leaving would then have minimal impact on trade between the two neighbors), the Scots already see Brexit as a blatant violation of a promise made by the Better Together campaign. If there is no second referendum on Brexit, there will likely be a second referendum on Scottish independence.

That's the thing about nationalism: It presumes a generally-agreed definition of the nation that is rarely agreed upon in practice. So Turkish nationalists must deny the reality of a Kurdish nation; Spanish nationalists provoke Catalan separatism; Ukrainian nationalists must pull away from Russia's embrace, and Russian nationalists must try to pull Ukraine asunder.

Understanding that doesn't make nationalist sentiment go away, because that sentiment springs from authentic sources. And managing that sentiment, the great challenge for liberal democracies today, requires a lot more than moral censure. But the nationalists themselves need to reckon with consequences that they rarely if ever acknowledge in their rhetoric — consequences for the integrity of the nation that they purport to revere.

The drama of Brexit has both revealed and deepened cleavages between the nations that make up the United Kingdom. They are unlikely to be knit up easily regardless of the outcome.