Getting Out: How Europe Can Defend Itself with Less America

This is a shortened version of a forthcoming CSIS report titled “Getting Out: How Europe Can Defend Itself with Less America.” 

With the war in Ukraine and the U.S. signaling a shift in its approach to European defense, Europe must proactively ensure its security. While the exact shape of the U.S. repositioning remains under development, the direction is clear: a greater emphasis on the Indo-Pacific and a corresponding expectation for Europe to shoulder more of the burden for its own defense. This shift is reflected in reports by think tanks aligned with U.S. President Donald Trump such as the Heritage Foundation’s Project 2025 and the Marathon Initiative’s “Resourcing the Strategy of Denial” report. U.S. Defense Secretary Pete Hegseth's prepared remarks at the February 2025 NATO Defense Ministerial emphasized that the United States "can't have the expectation of being [Europe's] permanent guarantor." The U.S. ambassador to NATO said in May 2025 that the United States will begin discussions with European allies to reduce U.S. troops in Europe later this year.

 A new era of transatlantic relations is emerging, demanding that Europe take greater responsibility for its own security.

This represents a structural shift in U.S. foreign policy, driven by the bipartisan focus on China as the primary challenge. The potential for a U.S.-China conflict would strain U.S. resources, limiting its ability to support Europe. Wargames conducted by CSIS suggest that the United States would run out of essential munitions – particularly long-range missiles – within a few days of entering a conflict with China over Taiwan. This would severely limit Washington's ability to supply Europe with certain critical munitions in the short-to-medium term. A new era of transatlantic relations is emerging, demanding that Europe take greater responsibility for its own security.

The Challenge: A Reduced U.S. Military Footprint

The current U.S. force posture in Europe effectively provides Europe with a lethal, high-end, full-spectrum, pan-European force. However, considering a potential imminent reduction to the U.S. military footprint on the continent, the most acute capability gaps for Europe would include:

• Ground forces: The U.S. Army, with roughly 80,000 servicemembers stationed in Europe at an array of bases, provides a de facto rapid reaction force for Europe. Redeployment of heavy combat formations, such as Armored Brigade Combat Teams (ABCTs) equipped with M1 Abrams tanks and Bradley Fighting Vehicles, would leave a significant void.
   
• Follow-on forces: NATO's rapid reinforcement strategy relies on the U.S. to provide high-readiness follow-on forces. A U.S. disengagement would require Europe to rethink both its reinforcement strategy and its infrastructure networks to sustain new supply routes.
   
• Air power: Europe relies on U.S. aircraft for air dominance and long-range strike. The U.S. maintains a substantive fleet of fighter, attack, and transport aircraft in Europe, in addition to a U.S.-based bomber fleet used for the U.S. strategic nuclear posture, and which serve as the delivery vehicles for advanced air-launched cruise missiles.
   
• Naval power: A reduced U.S. naval presence would diminish NATO's deterrence in key maritime regions, particularly the North Atlantic and the Mediterranean.
   
• Missile defense: The U.S. Aegis Ballistic Missile Defense System, deployed on U.S. Navy warships, plays a pivotal role in regional missile defense. The United States also deploys ground-based Patriot missile defense systems across NATO’s eastern flank, including in Poland and Romania.
   
• Military enablers: Europe depends on the U.S. for critical logistical support, including airlift and air refueling. To operate an air war against Russia, air refueling is vital to keeping fighter jets aloft and extending their range. Moreover, Europe is utterly reliant on the U.S. defense industrial base after prioritizing critical U.S. systems over European alternatives for decades.
   
• Intelligence, Surveillance, and Reconnaissance (ISR): Europe faces significant gaps in ISR capabilities, particularly space-based assets. For example, the United States operates 246 military satellites, far outpacing the 49 satellites managed by European NATO members.

Deterring Russia without the United States

The sudden withdrawal of U.S. forces, combined with a decline in the intensity of the fighting in Ukraine, would create significant dangers for Europe. Various European intelligence agencies estimate that Russia could reconstitute its armed forces relatively quickly, while Russia's wartime economy will likely continue unabated regardless of circumstances in Ukraine. 

Russia's full-scale invasion of Ukraine also highlights the potential danger of a conventional land invasion of NATO and European states. European forces may have an early advantage, pummeling Russia's initial invasion force. But Europe would quickly run short of munitions and frontline forces, swinging the advantage dramatically back in Russia's favor. While Russia's air power has been of limited effect in Ukraine, European war planners cannot assume that will be the case should Russia attack NATO and the EU. Russia's air force includes approximately 1,400 combat-capable aircraft, many of which are modern, such as the Su-35 and Su-57.

Transforming European Defense: Key Tasks

Europe must undertake bold action to ensure its security. This requires Europeanizing Europe's disparate militaries, such that Russia is confronted not by a loose collection of individual states but by a collective and united Europe. To do this, Europe should undertake five tasks to ensure its security:

• Task 1: Create a pan-European force of 100,000 troops. With 1.86 million active military personnel across European NATO countries, it is striking that the departure of fewer than 100,000 U.S. troops might create a strategic vacuum. To replace U.S. ground forces in Europe will require Europeans to maintain a force of roughly similar strength that is ready and able to immediately deploy to defend the eastern flank. This force should be made up of troops sourced largely from non-frontline states, particularly Europe's south, and led by a framework nation like Spain or Italy.
   
• Task 2: Integrate procurement to operate same equipment. The 2025 NATO summit in the Hague focused on increasing European defense spending, but there has been little discussion about reforming how Europeans spend. Fragmented national procurement means that Europeans do not leverage their collective size and purchasing power to create economies of scale. Solutions could include empowering the European Commission to leverage joint borrowing or establishing a new European procurement authority.
   
• Task 3: Prepare for attritional warfare by expanding stockpiles. Once Europe fixes how it procures, it needs to build stockpiles of weaponry and boost its defense industrial capacity to produce those weapons. Europe needs a wide range of equipment: artillery, long range strike capabilities, air defense systems interceptors, armored vehicles, and UAVs.
   
• Task 4: Mitigate dependencies on U.S. enabling capabilities. There remain critical domains – including air-refueling, air-transport, integrated command-and-control systems, and intelligence, surveillance, and reconnaissance (ISR) – in which continued U.S. involvement is vital to Europe's defense. European forces could operate without U.S. capabilities, but their operations would face significant challenges, requiring on-the-fly reforms and improvised solutions. Nevertheless, it makes sense for Europe to work over the medium-to-long term to reduce its dependence and build its own enabling capabilities while ensuring compatibility with the United States and NATO partners. This effort should include rapidly procuring additional air tankers and air lift assets, building out European ISR capabilities, and integrating European military intelligence structures.
   
• Task 5: Build redundancy into European command structures. While Europe can likely count on NATO command structures in the short term, European countries may want to plan for a contingency in which they would be required to run a war with limited support from the United States. Europe has at least three options:
   
  • Option A: Europeanize NATO. These efforts include a deeper conversation about Europe’s nuclear umbrella in order to transition from a US to a European SACEUR; installing more European military leaders in NATO’s regional commands; and leveraging the European Union’s fiscal capacities to support NATO activities.
     
  • Option B: Institutionalized “Coalitions of the Willing” and Sub-Regional Coalitions. Europe could utilize coalitions of the willing and regional groupings, if NATO becomes inoperable. A main benefit of the coalitions concept is that it can exclude unwilling or reticent countries like Hungary and would be directly focused on the specific warfighting task.
     
  • Option C: Build out the European Union’s defense structures. European countries could prioritize building on existing EU efforts that could provide redundancy to NATO’s Allied Command Operations (ACO). This could include vesting the EU Military Staff with greater competences and investing greater resources into the Military Planning and Conduct Capability.

Conclusion

Growing military capability gaps in Europe and the potential consequences of a significant U.S. drawdown of forces and equipment from the continent demand urgent action. Translating this strategic risk into concrete action will require European leaders to build consensus for a defense reform agenda. Furthermore, while the European Union should become a strong driver of European defense integration, Europe’s defense transformation should also include non-EU countries critical to Europe's defense, such as the United Kingdom and Norway. Lastly, the United States should shift its diplomatic focus from pressuring Europeans on simply increasing defense spending to insisting upon European defense reform.