NATO's expansion and increased defense spending enhance European security

What's this about?

People disagree about whether NATO’s growth and higher defense funds make Europe safer.

The best proof shows gains for NATO members, but the wider effect stays unclear.

What supporters say

• Shared defense may stop attacks because an enemy may face all NATO members.
• Higher spending can help troops get ready, hold more gear, and work well together.
• States seek NATO membership because they see it as a way to gain safety and strong ties.

What critics say

• NATO’s growth may raise fear in other states, which can cause more arms and more risk.
• More arms do not promise peace, since leaders can still choose to fight.

How to read this

The number of points on each side does not show which side is right; strong proof matters more.

The bottom line

NATO growth and higher defense funds likely help protect its members.

But we are not sure yet that they make all of Europe safer, and more arms may raise risks.

NATO’s expansion and higher defense spending may make Europe safer, but the effect is not automatic. The evidence is strongest for protecting alliance members and improving military readiness; it is less conclusive on whether these policies improve security across Europe as a whole.

The case for

The clearest argument is collective defense. If an attack on one NATO member is likely to bring a response from all, an aggressor faces much higher costs. NATO identifies deterrence, defense and cooperation as central purposes, and peer-reviewed research suggests that changes to the alliance’s military posture can improve its resilience. Public support for helping an ally under attack can also make those promises more believable. 1

That evidence supports a strong strategic logic, but it does not show exactly how many conflicts NATO has prevented. Deterrence is partly measured through events that never happen, making its effects difficult to observe directly.

Higher defense spending can also improve security when it produces usable military capabilities, rather than simply larger budgets. Spending on readiness, ammunition stocks, transport, surveillance, mobility, forward defense and forces that can work together may improve the alliance’s ability to respond to a crisis. NATO’s own materials make this connection, although the alliance’s institutional role limits their independence when they are used to judge NATO policy. 2

The benefits of membership are also reflected in the choices of states seeking to join. NATO expanded substantially after the Cold War, and analysis of Ukraine’s strategy toward Europe and NATO suggests that governments may view integration as both protective and institutionally valuable. This shows that applicants perceive security benefits in membership, though it does not prove that enlargement has improved security for Europe overall. (see Figure 1) 3

The case against

The strongest challenge is that enlargement can intensify a security dilemma. Expanding NATO may reassure new members while increasing threat perceptions in Russia and nearby states. The cited studies argue that eastward expansion encouraged reciprocal military behavior, especially where Russia viewed the alliance as offensive rather than defensive. This is a plausible pathway to greater tension, though the evidence does not establish that enlargement was the main cause of the war in Ukraine. 4

Military strength also does not guarantee peace. Deterrence may prevent some large-scale attacks while failing to stop limited wars, coercion, miscalculation or escalation. Strategic assessments generally present stronger defenses as a response to a dangerous environment, not proof that spending itself made the region safer. 5

The impact of spending depends on quality, coordination and burden sharing. Uneven commitments between allies can limit the value of higher national budgets. Targeted investment that improves readiness and interoperability is better supported than the idea that any increase in spending automatically enhances security. (see Figure 3)

The bottom line

The evidence favors a qualified version of the claim, with high confidence that credible collective defense and well-directed military investment can protect NATO members and strengthen deterrence. It offers only moderate confidence, however, that enlargement and higher spending have improved security for Europe as a whole.

The central uncertainty is whether the gains for protected members outweigh the tensions and costs imposed on the wider region. The available research does not provide a common comparison showing what European security would have looked like without NATO enlargement or with different spending choices. It also cannot fully separate NATO’s effects from Russian decisions, other national policies and broader competition among major powers.

The most defensible conclusion is conditional: NATO enlargement and defense spending can enhance security when commitments are credible, capabilities are coordinated and the alliance’s posture deters rather than fuels escalation. Enlargement or higher totals alone do not prove a net security gain for Europe. (see Figure 4)