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There is no official data on the scale of military support the United States would contribute to NATO in the event of a continent-wide war with Russia. However, according to IISS analysts, NATO remains heavily reliant on U.S. strategic intelligence, space and cyber capabilities, and its vast nuclear arsenal, particularly through U.S. European Command (EUCOM):
“In the event of conventional operations in Europe to counter Russian aggression, the U.S. would likely contribute around 128,000 personnel, along with land, sea, and air units.”
The third section of the IISS report focuses on the potential consequences of a U.S. withdrawal from NATO and Europe.
Assuming this scenario, highly complex and time-consuming though it may be, is treated as a real possibility, the simulation presented by IISS experts is divided into two main strands.
In the first scenario, existing U.S. bases, training areas, and military infrastructure in Europe could be sold to host nations or commercial buyers. Surplus ammunition and spare parts might be handed over to European militaries. However, European states would be required to replace the advanced training facilities, teams, and tools currently provided by the U.S. in forward-deployed locations.
The second scenario considers a reduction in U.S. intelligence sharing, which would expose gaps in Europe’s space-based and all-domain Intelligence, Surveillance, and Reconnaissance (ISR) capabilities. This would significantly impair Europe’s ability to detect early signs of a Russian attack and to interpret Russian military plans once hostilities begin.
According to the report, if the U.S. were to fully withdraw from Europe, the financial burden on European countries to replace American capabilities on a one-to-one basis would amount to between $226 billion and $344 billion. This figure excludes the cost of intelligence, space, cyber, and nuclear capabilities.
When accounting for one-time procurement costs and 25-year lifecycle expenses, IISS estimates that fully replacing the U.S. role in NATO’s collective defense would cost Europe close to $1 trillion.
This staggering cost is one of the key reasons for European officials’ anxiety over a possible American exit.
IISS analysts argue that even if Europe could afford the financial burden, its defense industrial base currently lacks the production capacity to meet the demand. The report explains:
“European defense firms have begun expanding capacity, opening new assembly lines and engaging in mergers and acquisitions, but progress is uneven, and many structural issues remain unresolved.”
“Should European allies decide to invest in additional aircraft carriers or nuclear-powered attack submarines (SSNs), delivering them would be a major challenge.”
“In the short term, European manufacturers will struggle to meet the necessary volume of armored vehicles, given current production limitations. Therefore, states must significantly invest in expanding their land systems industries, repurposing facilities from other sectors and striking new deals with long-standing suppliers like the U.S. and Canada, as well as non-European armored and artillery manufacturers.”
The report also points out that because procurement in most European countries is handled at the national level, order volumes remain small compared to the U.S. To address this gap, the IISS recommends pooling orders through international cooperation to achieve economies of scale.
The financial burden of filling that gap, combined with the prospect that Russia could rebuild its ground forces by 2027 if a ceasefire is reached in Ukraine, has set off alarm bells across the continent.
Under current conditions, even scaling Europe’s defense industry up to the level of Russia’s so-called “war economy” would fall short. Structural hurdles, ranging from workforce shortages to production bottlenecks, fragile supply chains, and limited financing, remain daunting. Take, for example, a single figure from the report: ordering an additional 400 fighter jets alone would overwhelm the world’s current production capacity.
Escaping this bleak scenario will require Europe to go far beyond current commitments. Defense spending will have to increase further. Joint (multinational) procurement of weapons systems must become the norm. Public financing will be needed to ease the fiscal burden, and governments will need to persuade their citizens to accept it. Bold financial-industrial initiatives, innovative public-private investment models, and hard choices about spending priorities will all be essential. Yet even if the money is found and capabilities are built, one challenge looms larger than all others: forging genuine political unity and collective will. That may prove the hardest task of all.
Already, aid to Ukraine, at today’s levels, has fueled political turbulence across Europe, where governments are grappling with migration, climate, and economic crises. The rise of the far right, a trend that European capitals are watching with growing unease, is gaining traction by channeling widespread demands for stability and security, and is beginning to topple governments.
