What will Brexit mean for European security? 

Despite the tensions generated by Brexit, the leaders of France, Germany, and the United Kingdom have stood together in disputes between the European Union and the United States. If their unity can be sustained, Europe’s “big three” (E3) will serve the EU very well in a tumultuous future.

French President Emmanuel Macron, German Chancellor Angela Merkel, and UK Prime Minister Theresa May seem to have read from the same script regarding US President Donald Trump’s withdrawal from the Iran nuclear deal and his rejection of the final communiqué of the G7 summit in June. They all disapprove of Trump’s decisions to move the US embassy in Israel to Jerusalem and to withdraw the US from the United Nations Human Rights Council. And they have all criticized his escalating trade war with China.

This unity is not merely rhetorical. The UK has lately supported EU integration projects concerning foreign and security policy – much more so than before the Brexit referendum. This includes the decision to establish new headquarters for military training missions – which many view as the nucleus for a potential European military – in Africa. Britain had long resisted this initiative.

The catalyst for the UK’s change of course, it seems, is Trump. There is significant evidence suggesting that Trump views the EU and some of its member states as adversaries, rather than allies. While the US will remain the most important ally of the EU and NATO’s European members, it is no longer the most reliable one. This shift has dashed hopes in the UK that post-Brexit Britain would be able to capitalize on its “special relationship” with the US, and it has highlighted for the EU the urgency of increasing its own strategic autonomy.

While the North Atlantic alliance will remain critical to European security, the EU now seeks to build the capacity to define its own strategic priorities and, if needed, act upon them, whether alone or with partners. Achieving this objective, defined in the EU’s 2016 “Global Strategy,” will be much easier with the UK on board.

The fact is that the EU and the UK have more international clout together than separately. The UK has significant diplomatic experience, international influence, and military and economic resources that can be brought to bear on joint ventures, just as the EU’s backing can provide a major boost to UK policies on the world stage. This applies to démarches regarding major actors like China or Russia, sanctions regimes, international agreements, and strategic programs like Galileo, the European satellite navigation system.

How exactly a post-Brexit UK can be institutionally associated with common EU decisions on foreign policy, security, and defense will have to be determined in the exit agreement. But it is possible to create a format that gives the UK a voice, not a veto. In the meantime, no decisions should be taken that would prevent or undermine the UK’s post-Brexit coordination with EU foreign-policy positions, actions, and instruments. Moreover, steps can and should be taken today to strengthen ties between the EU and the UK.

Here, collaboration among the E3, in particular, is crucial. The E3 has already proved its potential. It initiated negotiations with Iran over its nuclear program as early as 2003, and became the nucleus of the E3-plus-3 (China, Russia, and the US), which – along with the European Union – concluded the Joint Comprehensive Plan of Action (JCPOA) with Iran in 2015.

In the wake of Trump’s decision to withdraw the US from the JCPOA, the E3 – together with the EU’s High Representative for Foreign Affairs and Security Policy – will prove integral to saving it, and to developing more wide-ranging solutions for dealing with Iran. But the E3 has an important role to play in other areas, too, including the conflicts in Syria and Yemen, the ongoing Israel-Palestine dispute, instability in North Africa, and maritime security in the Mediterranean, the Indian Ocean, and the South China Sea.

Depending on the issue, other relevant EU member states – such as Italy, Poland, or Spain – will have to join the E3 in developing policies or negotiating agreements. E3 initiatives should always be coordinated with the EU’s high representative, in order to take full advantage of the bloc’s legitimacy and resources.

More frequent and visible strategic coordination among the E3 would support the ability of the EU and the UK to reap the benefits of mutual cooperation. It may also serve as a foundation for a pragmatic Brexit agreement that maintains close cooperation between the UK and the EU on foreign and security policy.

Whether the EU likes it or not, a credible joint initiative by France, Germany, and the UK would have a greater impact on the likes of Iran, Russia, China, or even the US than a common EU position emanating from a debate in the EU’s Political and Security Committee. Fostering deeper E3 collaboration, of the kind that has been seen recently, must remain at the top of the EU’s foreign-policy agenda before and after Brexit.

The fact that France, Germany, and the UK will all be members of the UN Security Council for the 2019-2020 period – France and the UK as permanent members, and Germany as an elected member – will add heft to cooperative action among them. Moreover, close collaboration within the Security Council could help to structure EU-UK foreign-policy coordination in the immediate post-Brexit transition period.