Security Guarantees by Proxy: The Incompatibility of European Commitments to Ukraine and the US Role in NATO
As competing peace proposals change hands and negotiators meet to discuss an end to the Russia-Ukraine conflict, the issue of security guarantees remains a sticking point. While the Trump Administration remains firmly against NATO membership for Ukraine, European efforts to extend security guarantees risk dragging the United States into a potential future confrontation with Russia. If European countries offer a treaty commitment to Ukraine, the United States may need to reassess and redefine its own security commitments towards Europe.
The North Atlantic Treaty’s Article V states that an armed attack against one member shall be considered an attack against all members. Beyond that, however, the treaty remains ambiguous. European offers of security commitments for Ukraine, even in the face of US opposition, risks producing a security guarantee by proxy as the United States may be called to defend allies that would be fighting on the side of Ukraine against Russia.
For decades, the United States has successfully maintained treaty alliances with countries around the globe while simultaneously largely avoiding interregional entanglement. The fact that the United States has defense pacts with Spain, South Korea, and New Zealand concurrently does not fundamentally complicate the security of the latter due to the highly regional nature of the various relationships. Should Washington’s transatlantic allies pursue a new and additional alliance on NATO’s doorsteps, however, the delineations would begin to fade.
Efforts to establish a so-called “Coalition of the Willing” to deploy in Ukraine along with European security guarantees can only be credible if Kiev’s allies are prepared to go to war with Russia. However, their unwillingness so far to join the fighting, materiel shortages, and the fact that their militaries are smaller than the Armed Forces of Ukraine makes it far from credible. As things currently stand, the Kremlin does not seem to be intimidated by European troops, with President Vladimir Putin recently saying, “Russia does not intend to fight Europe, but if Europe starts, we are ready right now.”
While European deployments to Ukraine may be seen as an effective deterrent that ensures the security of NATO’s European members, it would in fact strain their capacity to provide for their own security. Proposals in the spring included a European force of up to 50,000 troops to be deployed in Ukraine. In such a scenario, these very same countries may look across the Atlantic for added protection to make up for their shortfalls. This would undermine official US policy, as per the 2025 National Security Strategy, which includes “[e]nabling Europe to stand on its own feet and operate as a group of aligned sovereign nations, including by taking primary responsibility for its own defense.”
If European countries find themselves in a shooting war with the Russian Federation, ostensibly in defense of Ukraine, fighting can quickly spill over into NATO territory, some of which host US forces. The US government could argue that it is not required to come to the aid as it is not a party to a Ukraine-centred alliance and that the Europeans were partially responsible for the outbreak of hostilities but that may prove to be too little, too late as Moscow would understandably remain skeptical about an American ability to remain outside of such a war.
In fact, European leaders may be hoping that by linking Ukraine’s security to that of NATO members’ (even if formally outside the alliance) that the United States will find itself committed by a fait accompli. To avoid this, the White House needs to clarify what Article V will mean in case European countries decide to extend security guarantees unilaterally to Ukraine.
The United States needs to communicate to its European partners clearly that security guarantees for Ukraine would fundamentally alter the threat of war to NATO in general and the United States in particular. This includes ruling out applying Article V on NATO territory should these European countries be involved in active fighting against Russia on the soil of a third party.
The United States could withdraw its forces from Ukraine’s formal allies, especially those situated close to Russia, in order to minimize the possibility of being caught in the crossfire. There is already a desire in the Executive Branch to reduce troop levels on the continent, such as when the Pentagon announced plans in October for a drawdown in Romania.
European countries will then need to make a decision: do they prefer preserving a military alliance with the United States or become non-credible guarantors for Ukraine?
Having divergent interests is normal and can also be healthy. However, this is not compatible with an all-encompassing alliance which positions itself as the only tenable continent-wide security organization. Instead, the United States and its European allies need to be honest with each other and with themselves on what European security guarantees would actually mean for NATO.
The core risk here isn’t just proxy guarantees, it’s the breakdown of legibility inside alliance commitments.
NATO worked because Article V compressed intent, capability, and response into a single, readable signal. European security guarantees to Ukraine fracture that compression without replacing it with a new one.
The result isn’t deterrence or restraint, but strategic opacity: actors can’t tell what triggers what, or who is actually committed to whom. That’s when miscalculation becomes more likely than deliberate escalation.
The issue isn’t European ambition or American reluctance, it’s that post-Cold War alliance structures are being asked to carry commitments they were never designed to make intelligible.