It is February 2021. A few months after his re-election as president of the United States, Donald Trump declares that NATO has become obsolete and the United States withdraws from the alliance. All U.S. forces — military personnel and equipment — including nuclear and missile defense assets will be withdrawn from Europe as soon as possible.

This nightmare scenario has been on the mind of many security policy officials, and experts, ever since the New York Times reported in January 2019 that Trump discussed several times over the course of 2018 wanting to withdraw from the alliance. Congress has acted and passed the NATO Support Act, which prohibits the use of funds to withdraw the United States from the North Atlantic Treaty Organization. Yet the possibility of such a move cannot entirely be excluded.

Trump’s musings about a NATO withdrawal have served as a wake-up call for some in Europe that Europeans urgently need to assume greater responsibility for their own security. This realization is one of the reasons why closer defense cooperation and a greater degree of strategic autonomy are high on the European Union’s agenda. But are Europeans able to defend themselves? How would they think about their defense without the United States?

A policy game prepared by Körber-Stiftung and the International Institute for Strategic Studies sought to answer these questions this summer in Berlin. Five country teams with experts from France, Germany, Poland, the United Kingdom, and the United States addressed a fictional scenario that involved a U.S. withdrawal from NATO, followed by crises in a NATO member state in the western Balkans and across Eastern Europe. How would Europeans react to such a scenario? What are the red lines, interests, and priorities of the respective actors? How might Europeans organize their defense if the United States withdraws from NATO, and what role could the United States play in European security after the withdrawal?

The results of the game were sobering, with no clear upside for any of the participating teams. While a one-time simulation exercise, it provided valuable insights into the interests and preferences of European member states.

At the beginning of the policy game, most European teams adopted a “wait-and-see” approach focused on persuading the United States to return to NATO, offering concessions that were unthinkable before (from trade to energy). The unfortunate message for transatlantic relations seems to be that a threat to abandon NATO might actually yield some results.

Europeans started to take proactive steps only once the security situation in the scenario deteriorated significantly, and when it became clear that the U.S. withdrawal decision — at least in this simulation — was irreversible. Faced with a crisis in a NATO member state in the western Balkans (in the scenario, a pro-Russian coup d’état with Russian warships blocking access to the Mediterranean Sea), most teams anticipated that remaining NATO members would struggle to agree to invoke the principle of collective defense under Article 5 in this grey-zone scenario. Instead, the invocation of Article 4 — which involves only consultations in case the security or independence of a NATO member state is threatened — paired with sanctions on Russia and a robust response within ad-hoc coalitions were the preferred means of action. Without U.S. security guarantees, it seems, the credibility of Article 5 and the mutual defense commitment are questionable.

And then it got worse: In case of an escalation in the east (an incident akin to the Cuban missile crisis, involving an extended-range version of the SSC-8 Screwdriver land attack cruise missile with a range in excess of 4,500 km stationed in western Russia), European shortfalls especially in air and missile defense were identified as an existential risk for European countries without nuclear capabilities after the United States has withdrawn all nuclear and missile defense assets in the scenario. Given that filling these gaps would require long-term investment, Europe would likely remain vulnerable for years to come in such a scenario.

Especially for Germany, a U.S. withdrawal from NATO would represent an existential security threat. The German team suggested exploring the possibilities of the Franco-German Aachen Treaty of 2019 and asking France and the United Kingdom to expand their nuclear umbrellas to other European countries. Developing a German nuclear weapons capacity was considered an unlikely option, due to domestic opposition. Yet, expanding the British and French nuclear umbrella would come at a significant cost: The burden-sharing debate would return to Europe. Nuclear deterrence will remain the Gretchenfrage of European security, and if expanding the British and French nuclear umbrella fails, some teams anticipated a proliferation of nuclear weapons in Europe.

When it comes to institutional frameworks, from a French perspective, NATO would be dead without the United States: The French team preferred a new, E.U.-centered collective defense structure in the long term, with other actors affiliating on a bilateral basis. This position was met with skepticism especially from the British and Polish side; Germany, Poland, and the United Kingdom were adamant that the NATO command structure should be maintained after a U.S. withdrawal and provide possibilities for the United States to “opt in” to any future security structure.

A post-Brexit United Kingdom, as envisioned in the scenario, would consider itself a leading actor in European security, willing and capable of shaping Europe’s future security architecture. Given its significant defense capabilities, the U.K. team saw its country in a powerful negotiating position and was skeptical of French and German leadership on defense issues. British red lines were the following: No E.U. army, no E.U. alliance or, as they said, the United Kingdom wants to design European security, not just sign on a dotted line.

As the representative for NATO’s most vulnerable-feeling eastern member states, the Polish team did not trust Europe’s ability to organize collective defense and was tempted to conclude bilateral deals with the United States. As the Polish team said, if the United States withdraws, the eastern flank should be the last place. A “bilateralization” of security and defense with the United States, including bilateral security guarantees, is the likely consequence. Interestingly, all teams rejected Russian overtures for conflict resolution in exchange for concessions on security, such as drafting a European security treaty based on Medvedev’s 2008 proposals. This demonstrates that Russia was not considered a credible security provider in Europe, despite suspicions that Germany might be tempted to engage in a dialogue with Russia on this.

For the U.S. team, subsidizing European security was no longer an option. The team felt that Europeans should put everything on the table for security guarantees, from trade to policy alignment on Iran and China. The U.S. team argued that countries that care will find a way to keep the United States engaged, and that Europe should take the lead in crisis management on the continent. In this scenario, a transactional relationship seems to be the new normal in U.S.-European relations, yet Europeans were disillusioned as they hoped for a continuous strategic U.S. interest in Europe and a values-based partnership. In contrast, the U.S. team in the game focused primarily on a fair deal addressing both defense and trade issues.

Thinking about the broader implications of the policy game, it becomes clear that without U.S. security guarantees, the principles of European unity and mutual solidarity were quickly challenged and Europe was at serious risk of splitting into different camps. While Europeans were in principle willing to organize their own defense, the shortfalls in military capabilities precluded meaningful action and led to a quick emergence of divisions. This could also occur under conditions short of U.S. withdrawal, such as a reduction in its European force posture or its willingness to engage. Any degree of reduced U.S. commitment would thus exacerbate European divisions.

Better to Be Prepared than Sorry

What should Europeans do to step up and prevent this outcome? Here are a few recommendations that emerged during the policy game:

Engage the public in a sustained debate about security and defense in Europe. This strategic communication will not necessarily translate into support for specific policy choices advanced by governments, but it will serve as a bulwark against misinformation as well as populist arguments and enhance societal resilience.

Think about the unthinkable. Two assets that are of critical importance to the ability of Europeans to defend themselves are the NATO command structure and the extended nuclear deterrence provided by the United States. If these were to be withdrawn or dismantled, Europeans would immediately have to provide alternatives.

Invest in European military capabilities and the mechanisms to deploy them. This is necessary to hedge against U.S. disengagement while providing a greater share of NATO’s collective capability. This would make it less likely that the United States decides to leave while also making Europe more self-sufficient in case America does disengage.

Strengthen efforts to reassure Eastern European member states. European solidarity should be expressed in terms of measurable commitments to those countries’ security. Already, diverging threat perceptions are a source of weakness, both for NATO and the European Union.

Accept that building European military capabilities and creating a convincing deterrence and defense posture will take more than a decade and will require sustained financial investment. There are no shortcuts to credibility.

Lastly, should Europe face a situation when the United States indeed withdraws from NATO, adjusted and strengthened European security structures should provide mechanisms for the United States to contribute to European security on a “plug and play” basis. In the short term, this will help to keep America engaged, to maintain Europeans’ focus on military interoperability with the United States, and to facilitate a maximum level of transatlantic political cohesion. In the long term, it may lower the hurdles for re-engagement and would serve as an important reminder that even a withdrawal can be reversed.

Liana Fix is program director for international affairs at Körber-Stiftung’s Berlin office with a special focus on Russia and Eastern Europe. Previously, she was a doctoral fellow at the German Institute for International and Security Affairs. She holds a master’s degree in theory and history of international relations from the London School of Economics and Political Science and concluded a Ph.D. on Germany’s role in European Russia policy. Liana publishes on topics related to European security, Russian foreign policy, and Eastern Europe.

Dr. Bastian Giegerich is the director of defense and military analysis at the International Institute for Strategic Studies (IISS) and leads the team that produces the annual flagship publication The Military Balance. From 2010–15 Bastian worked for the German Federal Ministry of Defence in research and policy roles, while also serving as the IISS consulting senior fellow for European security. Bastian is the author and editor of several books on European security and defense matters.

Please note that the results of the Körber Policy Game presented in this article reflect the analysis of Körber-Stiftung and IISS and not necessarily that of the participants.

Image: U.S. Air Force (Photo by Staff Sgt. Victor J. Caputo)