Can a single public vote undermine a century of cooperation and friendly rivalry? Was the Brexit referendum indicative of a long-running shift in the United Kingdom’s relationship with the Continent, and especially with allies like France? Britain and France were competitors, and even enemies, for almost a millennium before they allied, first to contain Russia in the Crimean War, and then to prevent German dominance of Europe in the two world wars. But now, France is taking the hardest line among European Union members in Brexit talks. French President Emmanuel Macron has called Brexiteers “liars,” while the British press has accused France of trying to inflict maximum pain on British citizens and trap the U.K. in its orbit.

Those in favor of Brexit saw the vote as an opportunity to escape what they perceived to be an increasingly authoritarian, German- and French-dominated bloc – one that they believe is determined to punish the U.K. for the trouble it’s caused on the way out. The pro-Europe French perspective, on the other hand, sees the British departure as opening avenues for deeper Continental integration, especially in foreign policy and defense, in which Paris will be the leading voice. But beneath the daily scuffles over the backstop or backdoors into the EU single market, France and the U.K. have remained close on foreign policy and defense. They have too much strategic overlap, and too few alternatives, to drift apart.

This Deep Dive will consider the forces that pushed the two nations together and kept them close. Despite the U.K.’s effort to redefine its relationship with the Continent and secure its autonomy from Europe, and despite European efforts to deepen integration historically blocked by the U.K., Franco-British strategic cooperation will continue, mostly uninterrupted.

British Solitude

The United Kingdom is an archipelago of thousands of islands off the northwest coast of the European peninsula. It boasts an impressive population (66 million people in 2017), wealth (a gross national income of $2.58 trillion), nuclear weapons and one of the strongest armed forces in the region. These assets, paired with the advantage of physical separation from Continental challengers, once allowed the British Empire to rule the seas – and a quarter of the Earth’s land, too.

Yet, even at the height of its power, Britain had to stay abreast of developments across the narrow English Channel. It needed to maintain allies and a military able to prevent any single power from consolidating control of Europe and marshaling the Continent’s superior resources to threaten the British Isles. Its alliances shifted to balance whoever was most powerful, from Napoleon Bonaparte’s France to the Russian Empire. Containment of Germany has been the center of this balance of power strategy since 1870, when the German states unified (with a brief interlude during the Cold War). Germany’s population was larger than those of France and Britain. Its economic capacity outstripped France’s. And its geographic insecurity pushed it to expansionism.

But in the days after World War II – in the beginnings of the Cold War – something interesting happened. The largest Western European powers, France and Germany, and four other states decided to experiment with pooling their resources. Though initially surprised, British Prime Minister Clement Attlee welcomed the news. He saw it as a way to solve the German problem and help Western Europe’s economies rebuild from years of war. But over the next few years, as the European project trudged along, Britain’s economic interests and its concerns that it was being left out of important decision-making in Europe prompted it to reconsider its relationship with the European bloc. The United Kingdom decided it needed a seat at the table.

French President Charles de Gaulle thought otherwise. In 1963, and again in 1967, de Gaulle blocked British accession to the newly formed European Economic Community. For the French president, the EEC was designed in part to liberate Europe from Atlanticist hegemony. He would not open the gates to an American Trojan horse draped in a Union Jack.

The U.K. would eventually get its seat in 1973 – a few years after de Gaulle’s resignation. But the U.K. never fit comfortably at the table. And, realizing both de Gaulle’s fears and Britain’s grand strategy, the U.K. was able to disrupt European integration, to an extent. (A study by a group at King’s College London found that the U.K. voted against the majority on foreign and security policy more than any other member state. It blocked efforts to increase the European Defense Agency’s Budget and, even after the Brexit vote, threatened to veto various initiatives.) The U.K. held a referendum on its European Community membership just two years after joining, and it always strove to keep one foot in and one foot out. The beginning of the end came in the early 1990s. The U.K. accepted an opt-out from the Economic and Monetary Union in exchange for signing the Maastricht Treaty, which established the European Union. Two decades later, London was left out of key decisions on the eurozone and Europe’s future. A major argument for British membership in the European project had evaporated; the union increasingly belonged to Berlin and Paris.

So, Prime Minister David Cameron called the vote, and a slight majority of voters expressed a desire to leave. Selling a vision of life after Brexit was easy. The U.K. would re-emphasize its “special relationship” with the United States, deepen ties with NATO and expand its global presence through new military bases and trade agreements with the world’s most dynamic economies. Besides, it wasn’t certain that the EU would survive the U.K.’s departure, especially once other euroskeptic countries saw what life could be like on the outside.

That post-Brexit vision was flawed for two reasons. First, the EU has maintained a more-or-less united front in the Brexit negotiations. And the EU’s demise doesn’t appear imminent, especially not as a result of Brexit: The bloc’s remaining euroskeptics have, at least for now, almost unanimously ditched the idea of leaving the EU in favor of trying to reform it from within.

Second, and more important, complications arose in the special relationship. For example, the U.K., like the U.S., has an interest in fighting jihadist groups in the Middle East and Africa and maintaining Mideast stability. But as the U.S. is withdrawing from Syria and adopting a more hawkish policy toward Iran, the U.K. has special operations forces deployed in Syria, has said the fight against the Islamic State is not over and, along with the EU, is working to keep the Iran nuclear deal alive. And in some ways, the Iraq War altered the U.K.’s ability to follow America’s lead in the Middle East. Afraid to repeat the mistakes of that war, and wary of being seen as too obedient and eager to do Washington’s bidding, the House of Commons in 2013 voted against joining U.S.-led strikes in Syria.

The more fundamental problem with London’s shift toward Washington is that the U.K. is seeking deeper ties with the U.S. just as the latter is urging Europe to take responsibility for its own defense so that the U.S. can turn its attention to Asia. NATO is losing its purpose, and just this week, The New York Times reported that U.S. President Donald Trump privately discussed withdrawing from the alliance several times in 2018. NATO or not, the U.K. and U.S. still share concerns over Russian revanchism, and the U.K. will be a vital American partner in the region. But what the U.S. really wants is to convince the rest of Europe, especially the Germans, to build up their defenses on the Continent so the U.S. can reduce its own contributions. It’s doubtful whether the U.S. or U.K. could change minds in Berlin, but this painful separation between the U.K. and EU is unlikely to improve their prospects of doing so.

The U.K. also faces the challenge of being able to afford a military designed to fight America’s wars. When Cameron announced an 8 percent cut to the military budget in 2010, he described a force that was “overstretched, under-equipped and deployed too often” and “ill-prepared for the challenges of the future.” It’s one thing for the U.K. to fight terrorism alongside the U.S. in the Middle East or Africa; it’s quite another to increase engagement in Pacific theaters, especially for a navy that went seven years without an aircraft carrier in service and that has only 19 destroyers and frigates in service, a historic low for the Royal Navy. (Budget aside, it would be awkward for a post-Brexit U.K. to seek a free trade agreement with China while the U.S. is ramping up its activity in the South China Sea.) The National Audit Office warned last year that the Defense Ministry’s long-term spending plan was “unaffordable” and that the armed forces had serious personnel shortages. It also cautioned that the equipment program could face a 14.8 billion-pound ($19 billion) funding gap – roughly the cost of five Queen Elizabeth-class aircraft carriers. And the country’s former chief of defense staff said in June that the government had “slightly deluded the public” with a defense program it can’t afford. Notably, the NAO’s latest report makes no mention of Brexit or its potential effect on the U.K.’s economic situation.

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These issues aside, part of the value of the U.S.-U.K. relationship for Washington was that London provided a trans-Atlantic bridge to the EU. The U.K. served as a de facto representative of U.S. interests in Brussels, helping to keep the EU economy open and shape foreign policy objectives. Long before the Obama administration opposed a move toward Brexit, former U.S. Secretary of State Dean Acheson remarked that Britain’s “attempt to play a separate power role apart from Europe, a role based on a ‘special relationship’ with the U.S. and on being the head of a ‘commonwealth’ which has no political structure, unity, or strength” was “about played out.”

The notion that the United Kingdom can expand its global influence outside the structures of Europe is flawed. And, ironically, the nation with whom the U.K. is perhaps best aligned, the country best positioned to be a partner post-Brexit, may not be the U.S., but rather the new undisputed leader of European defense: France.

France and European Integration

France is not isolated the way the United Kingdom is. But its geography – walled in by mountains to the south and oceans to the southeast, north and west – affords it a semblance of protection on several sides. Its greatest strategic threats, therefore, come from the east. From its perch at the end of the North European Plain, France would be the last stop of any European force seeking to threaten the British Isles. Germany’s unification, then, was a natural boon to the Franco-British relationship.

After World War I, France tried (and failed) to cripple the German state. After the second world war, they opted instead to tie their futures together. French Foreign Minister Robert Schuman and diplomat Jean Monnet proposed the European Coal and Steel Community, binding together the coal and steel sectors of France and West Germany. The rest is history.

Almost 70 years later, a war threatening France along the North European Plain is unthinkable. France’s greatest strategic threat today is Russia. Russia’s recent moves in the Black Sea (and to a lesser extent in North Africa) and the threat that the Russian navy could break out into the Mediterranean demand France’s attention. Beyond Russia, France’s national security priorities are concentrated on the Levant and Sahel-Sahara regions. While Paris knows it can’t be everywhere at once, it is the de facto military leader of a supranational entity with well over 1 million troops at its disposal. (Though in 2016, the European Defense Agency estimated that barely 400,000 EU troops were deployable, and it’s up to member states if and when to deploy them.)

If a global Britain is the U.K.’s unrealizable dream for life after Brexit, France’s might be a European army. The fulfillment of a Gaullist vision of a France-led European foreign policy and of Europe as an amplifier of French influence has not been this close in decades, but it’s still far away.

EU defense cooperation started, ironically, with a Franco-British summit. Frustrated with Europe’s inability to keep the peace in the Balkans without the United States, London and Paris signed the St. Malo declaration in 1998, which stated the EU “must have the capacity for autonomous action, backed up by credible military forces, the means to decide to use them, and a readiness to do so, in order to respond to international crises.” Out of St. Malo came the Common Security and Defense Policy, the framework for all the integration that followed. Throughout the process, however, the U.K. stressed that European cooperation could not conflict with NATO.

Brexit prevents the U.K. from blocking initiatives it doesn’t like, including the one it fears most of all: a European army. To be clear, the challenges to creating an EU army are so immense that it is frankly an impossibility for at least decades – and probably longer. But it’s also true that common defense initiatives that the U.K. had blocked are now getting off the ground. And it’s reasonable to conclude that, should the U.S. ever leave NATO, the infrastructure it left behind could be absorbed under the umbrella of the EU. It wouldn’t even have to move its headquarters.

In June 2017, the EU set up a small military headquarters, the Military Planning and Conduct Capability, responsible for planning and executing missions. It has training missions underway in Mali, Somalia and the Central African Republic. In November 2018, the European Union agreed to expand the MPCC’s force size and mission scope. In June 2017, the EU established the European Defense Fund to coordinate and boost member states’ investments in defense research, development and acquisition. (The fund is still small: Its 13 billion-euro, or $15 billion, budget in the EU’s next seven-year budget is roughly a quarter what France spends on defense in a single year.) The initiative that has generated the most buzz, the Permanent Structured Cooperation, or PESCO, was launched in December 2017, enabling member states to voluntarily participate in joint projects ranging from development of a new armored infantry fighting vehicle to a school for intelligence personnel. This is a far cry from an EU army, but it was close enough that the U.K. had resisted before Brexit.

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These initiatives are attractive to France, especially the ability to share the costs of weapons R&D and manufacturing and to use Europe’s economy of scale afforded by PESCO and the EDF. France’s defense companies stand to benefit, especially since Brexit, in theory, disadvantages a primary competitor. This is why the French have resisted calls to permit third parties to participate in PESCO. While they finally acquiesced, the limits of participation have not yet been decided. For the U.K., joint weapons research and development would help overcome the country’s budget constraints. Some have speculated, for example, that the Future Air Combat System under development by France and Germany within the PESCO framework could eventually be combined with the U.K.’s Tempest project.

But on operational effectiveness, European cooperation is no substitute for what the British can provide. In June 2018, France, the U.K. and seven other European countries signed a letter of intent to set up a common intervention force, the European Intervention Initiative. (Finland became the 10th member in November.) In addition, the Franco-British Combined Joint Expeditionary Force, founded in 2010 with the Lancaster House treaties, is forging ahead despite Brexit and is expected to be combat capable by 2020. The U.K. is also moving forward with another joint expeditionary force involving Denmark, Estonia, Latvia, Lithuania, Norway, the Netherlands, Finland and Sweden. France agreed to send troops to support the force in exchange for British help transporting French soldiers in Mali.

A hiccup in Franco-British strategic relations in the next few months leading up to and after the U.K.’s official departure date from the EU would not be a surprise. Indeed, last spring the U.K. withdrew its pledge to lead an EU battlegroup in 2019. But Franco-British relations have survived serious disagreements in the past, such as when France refused to join the invasion of Iraq. At the same time that was happening, Paris and London were working on plans for a European rapid reaction force, which became the EU battlegroups, and working to jointly manufacture an aircraft carrier, an ambitious effort that ultimately failed.

The U.K. and France need to maintain good relations. They have some common interests, particularly in the fight against jihadist terrorism in places like Syria and North Africa.  (While the U.S. is drawing down its forces in Syria, France has said its special operations soldiers will stay, and the U.K., which also has special operations forces in the country, has said that “much remains to be done.”) For the U.K., giving France the help it needs would reduce Paris’ interest in fighting for more defense cooperation from EU partners. And it’s in the U.K.’s interest not to become too reliant on one ally, especially one going through the strategic rethink that Washington is currently in the midst of. For France, seeking out help from a military equal next door is much more hopeful than trying to change German domestic opinion about the armed forces. Despite the bumpy road to Brexit, we haven’t seen the end of French and British defense cooperation.