Then, Donald Trump was elected U.S. president. Trump has extremely low approval ratings in Europe, and some leading politicians publicly opposed his candidacy. Again, the European Union called for a "crisis meeting."
But it turns out that both Brexit and Trump's election could actually help save the European Union.
In five of the union's six most populous countries, E.U. approval is on the rise. The only country where support has fallen is Spain. In Britain, a majority of the population would now vote to stay in the European Union, new data by the Bertelsmann Foundation suggests.
So, why is that?
There are two likely explanations: the perception that Britain is failing to make its exit from the E.U. a success and fears over President-elect Trump's reliability as a core economic and military ally. The Bertelsmann poll was conducted before the November U.S. elections, but the outcome might strengthen E.U. approval in Europe further, particularly in the continent's east.
Britain slashes growth forecast
On Wednesday, the British government said it would have to borrow about $72 billion more over the next four years because of the economic fallout of the Brexit vote.
Ahead of the referendum, leading politicians and experts had warned that leaving the E.U. would leave British households worse off. Despite such warnings, support for Brexit was highest in some of the areas that could now be hardest-hit by the country's economic woes.
The first signs that Brexit could weaken the appetite in other E.U. member states to follow Britain emerged days after the referendum at the end of June.
As the British pound dropped to all-time lows, other nations took note. While more than 40 percent of Danes wanted an E.U. referendum before Britain decided to leave the union, support for such a vote has now declined by nearly 10 percentage points.
Could the British decision glue Europe closer together? Austrians will head to the polls next month to elect a new president, and it is likely that far-right candidate Norbert Hofer could win.
Hofer had previously demanded an E.U. referendum for Austria. But shortly after the Brexit vote — potentially amid fears that a shift in public opinion would cost him crucial votes — he indicated that being part of the European Union might not be so bad after all. At the moment, Hofer is only in favor of an E.U. referendum in case the bloc becomes more centralized. A look at opinion polls helps explain what might have caused that change of mind.
The election of Donald Trump has also raised fears in Europe that he could weaken NATO and strengthen cooperation with Russia, which is viewed as increasingly dangerous in E.U. capitals. Eastern European and Scandinavian nations in particular fear Russia's army and have so far comforted themselves with the presence of U.S. troops in the region.
Fears of Russia
Trump, however, has suggested he would only defend countries that allocate a set ratio of their GDP to defense spending. Nearly no E.U. member state fulfills that criterion.
German President Joachim Gauck this week was among those who have called for the country to focus more on its own security. His words were unusual for a German president: Most of his predecessors had advocated disarmament instead of more military spending. But Trump’s contradictory statements on that matter have raised worries that the United States might no longer be a reliable military ally.
As the influence of NATO could decline during Trump's presidency, smaller E.U. countries might increasingly have to rely on the European Union, which is pushing for stronger military cooperation on the continent.
So far, E.U. politics have often appeared far removed from the everyday lives of Europeans. The E.U., critics argued, cared more about regulating the size and shape of bananas than about fundamental issues facing citizens. A military threat could change that calculation and the reputation of the Brussels bureaucracy in European Union member states.
It is ironic that 2016, the year that appeared to be the beginning of the E.U.'s end, could in fact give the union its strongest boost.