Brexit – NATO saw renewed interest from member states; the European Union was discussing new levels of defense cooperation; and the United States was moving toward increasing its European commitments — all in response to what the alliance perceived as a resurgent Russian threat along the eastern flank.

But by the close of that year, Europe’s slow return to great power competition was thrown into chaos.

In the U.K., a referendum called by then-Prime Minister David Cameron delivered a shocking upset when the country voted to leave the European Union; the country is now on its third prime minister since the June 23 vote. And in November, Donald Trump, a confirmed Euroskeptic whose foreign policy trademark was brow-beating European allies for decades of declining defense spending, was elected president.

Now, on the eve of Brexit and with Trump’s reelection a real possibility, the future of European collective security is anyone’s guess. Will NATO maintain its relevance, or will hard feelings drive a wedge in the alliance? If a new framework for European security is forged, will it exist under an EU without Britain, and will the the former member have any say in the framework’s direction?

On the maritime front, if existing frameworks come under pressure, Brexit means Europe could stand lose some protection provided by the region’s most capable navy. And while the position of Britain’s government has been that its commitment to European security remains unchanged, what form that takes is unclear.

“What this raises is the question of the European Union versus NATO,” said Jerry Hendrix, an analyst with the Virginia-based Telemus Group. “And what is the difference of commitment to those two entities? Everyone says that they are firmly committed to NATO, but Brexit has raised a question about the future of Europe as a political entity.

“Everyone has relaxed on the idea that they are all together politically, which had contributed to the decline of spending on military forces,” Hendrix added. “And for years, Britain has been the preeminent naval power, but maybe Brexit forces France and Italy and Norway to step up their own naval spending?

Brexit, which new British Prime Minister Boris Johnson has promised will be delivered “do or die” on Oct. 31, threatens to upend what has been an expanding role by the EU in security matters, something that has been a growing part of the organization’s mission in recent years.

“The interesting dynamic in European foreign policy is the introduction of the EU into it,” said Bryan Clark, an analyst with the Center for Strategic and Budgetary Assessments in Washington. “It was never one of the original objectives of the EU common market; it [the original objective] was economic in nature. The foreign policy element has really emerged in the past five to 10 years as the EU’s expansion has become a tool of foreign policy, especially for countries in Eastern Europe, such as Ukraine.”

Questions about post-Brexit European security have no easy answers. (Christopher Furlong/Getty Images)

Questions about post – Brexit European security have no easy answers. (Christopher Furlong/Getty Images)

As the EU became more of an instrument of foreign policy than an economic approach, it undertook more military-style operations, such as a counter-piracy missions off the coast of Somalia and a refugee rescue-and-support mission off the coast of Italy. Those operations have drawn in countries, such as Sweden and Finland, that were hesitant to participate in NATO operations so as not to antagonize Russia.

“The EU gives countries this kind of fig leaf that they are participating in a military operation without being openly hostile to Russia, and to some degree Belarus as well,” Clark said. “And these operations show this kind of expanding role of the EU.

“Especially if you are a NATO country, the EU gives you a chance to do security operations that’s not tied to a war-fighting framework that a lot of people feel like is a holdover from the Cold War.”