The Kremlin’s invasion of Ukraine changed the conversation about transatlantic security relations. If Vladimir Putin’s goal was to fracture the West and create divisions within the European Union (EU) and NATO, he inadvertently achieved the opposite when Russia invaded its neighbor in February. Both EU and NATO member states have arguably shown the greatest cooperation since the end of the Cold War and the Russian president’s demand that NATO abandons its open-door policy has resulted in Sweden and Finland rushing to join the military alliance.

But while unity in condemning the Kremlin’s action among Western nations has been strong, the ability of the EU and NATO to work together to reinforce transatlantic and European security architecture remains in question.

In the late 1990s, the EU’s aspiration to become less dependent on NATO clashed with transatlantic security priorities. Madeleine Albright, then US Secretary of State, warned that European defense must not de-link from NATO, duplicate existing defense efforts or discriminate against non-EU members. Debates over the EU’s strategic autonomy have continued ever since, with member states such as France arguing for greater leadership in European defense, while US administrations complained Europe had been too reliant on American support. Although neither side advocated for European defense completely independent from NATO, debates over greater strategic autonomy and burden sharing have strained transatlantic relations. And despite the US shift of its defense posture to Asia to confront China, administrations have remained dubious over activities outside the Transatlantic alliance.

NATO and the EU have established cooperative systems since the Cold War and have sought to counter malign influence from Russia and China while working on capacity-building efforts, such as Operation Althea in Bosnia Herzegovina. Increased communication between officials has been used to build trust, and at the 2016 NATO summit in Warsaw, the two signed a joint declaration containing the most clear-cut statement on EU-NATO cooperation until this year’s invasion of Ukraine.

The declaration said the EU and NATO required “new ways of working together and a new level of ambition,” and would cooperate in training and exercises, utilize interoperability and share intelligence where possible. In March, the EU released its latest Strategic Compass which pledged to “strengthen cooperation with strategic partners such as NATO.” Whether these strategies translate into tangible action is yet to be seen.

The current reality is that cooperation between the EU and NATO on defense policy, particularly in light of the current war, remains limited as a result of divisions among members of both alliances. An Ipsos poll, for example, indicated support for diplomatic engagement with Russia is significantly greater in Italy, Germany, and France than in the US, while in May, Italy and Hungary publicly called for a ceasefire in Ukraine and peace talks with Russia. Although most European officials have since dismissed the possibility, talk of a ceasefire demonstrated a lack of cohesion over executive decisions, a challenge the EU has repeatedly faced. Similarly, splits over deployments persist in NATO, with Poland and the Baltic states demanding increased military presence in their nations while France, despite deploying battlegroups in Romania and Estonia, shares Italy’s skepticism that Russia would target NATO countries.

As the NATO summit in Madrid approaches this month, these need to be tackled and internal divisions addressed. Members must signal to Vladimir Putin that NATO is an alliance of democracies, like the EU, and they can work together for a common goal despite internal differences.

In the coming months, both the EU and NATO will be required to tackle tensions over defense policy. While the deployment of additional troops and equipment to the Eastern Flank, and increased defense spending seem assured, it must be clear who is in charge of strategic policy. And while the US very clearly desires a much greater contribution from better-armed European states, that process of rearmament is only just getting underway.

Most immediately, the EU and NATO must send a clear message to Russia that the West will continue to defend European security, aid the Ukrainian people, and make Putin a pariah until he stops this senseless war. But behind the scenes, the Transatlantic community must decide its future shape.

SaraJane Rzegocki  is a Program Assistant with the Democratic Resilience Program at the Center for European Policy Analysis (CEPA). She holds an M.A. in Political Science with a concentration in European Union Policy Studies from James Madison University.

Alvina Ahmed is a Project Assistant with the Atlantic Council’s Transatlantic Security Initiative, part of the Scowcroft Center for Security and Strategy. Previously, she was an intern with the Democratic Resilience Program at the Center for European Policy Analysis (CEPA).