The IISS has conducted an independent open-source high-level assessment of how the defence of Europe, and of European interests, would look if the United States had left NATO and did not contribute militarily.
The study applies scenario analysis – with scenarios set in the early 2020s – to generate force requirements, and assesses the ability of NATO’s European member states to meet these requirements based on data from the IISS Military Balance Plus online database. The cost of closing the identified capability shortfalls through equipment acquisition has been estimated.

The objective of the study is to enable informed policy dialogue both in Europe and in a transatlantic setting. The study explicitly does not intend to predict future conflicts nor the intentions of any of the actors involved. Neither does it wish to prescribe a certain path of action to be pursued by European NATO governments.

The first scenario examined deals with the protection of the global sea lines of communication (SLOCs). In this scenario, the United States has withdrawn from NATO and has also abandoned its role of providing global maritime presence and protection, not just for its own national interest but also as an international public good. It thus falls to European countries to achieve and sustain a stable maritime-security environment in European waters and beyond, to enable the free flow of international maritime trade, and to protect global maritime infrastructure. The IISS assesses that European NATO members would have to invest between US$94 billion and US$110bn to fill the capability gaps generated by this scenario.

The second scenario deals with the defence of European NATO territory against a state-level military attack. In this scenario, tensions between Russia and NATO members Lithuania and Poland escalate into war after the US has left NATO. This war results in the Russian occupation of Lithuania and some Polish territory seized by Russia. Invoking Article V, the European members of NATO direct the Supreme Allied Commander Europe (SACEUR) to plan Operation Eastern Shield to reassure Estonia, Latvia and Poland, and other front-line NATO member states, by deterring further Russian aggression. European NATO also prepares and assembles forces for Operation Eastern Storm, a military operation to restore Polish and Lithuanian government control over their territories.

Example map from the second scenario outlining the force requirements that describe a limited war in Europe, led by a state-level adversary. Report Part 3. Baltic flashpoint: a state-level attack

The IISS assesses that European NATO members would have to invest between between US$288bn and US$357bn to fill the capability gaps generated by this scenario. These investments would establish a NATO Europe force level that would likely allow it to prevail in a limited regional war in Europe against a peer adversary. The assessment does not cover a full-scale continental war in Europe.

Beyond identifying capability shortfalls, the study underlines the centrality of the NATO Command Structure. Without it, it does not seem feasible at this point for Europeans to attempt to run demanding operations of the kind considered in this paper. Another implication of this research is the enduring importance of the US in military terms for the defence of Europe. This study provides a reality check for the ongoing debate on European strategic autonomy. Its findings underline that it would be helpful for this debate to focus on the capabilities to tackle threats to European security, rather than on institutional engineering. If the funding to meet shortfalls were available, the IISS assesses that the recapitalisation across the military domains would take up to 20 years, with some significant progress around the ten- and 15-year marks. The reasons for this are limited production capacity; the time it takes to decide on and then produce equipment and weapons; recruitment and training demands; and the time it takes for new units to reach an operational capability.

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As a NATO member, the US provides a significant reservoir of capabilities on which US and NATO commanders can and would draw in a crisis. Some of the capabilities provided by US forces, such as logistics and sustainment for land forces, may be relatively straightforward if not cheap to replace.

However others are almost unique to the US, and it would be difficult to substitute European capabilities.

Part 5. Implications for Europe’s defence debate 09 May 2019

Ben Barry, Senior Fellow for Land Warfare

Douglas Barrie, Senior Fellow for Military Aerospace

Lucie Béraud-Sudreau, Research Fellow for Defence Economics and Procurement

Henry Boyd, Research Fellow for Defence and Military Analysis

Nick Childs, Senior Fellow for Naval Forces and Maritime Security

Bastian Giegerich, Director of Defence and Military Analysis