Would NATO Fight if Russia Crossed Its Border? A Former Commander Answers

Russian troops crossing into NATO territory would be met with an immediate response from alliance forces stationed along the eastern flank, according to Skip Davis, a retired US Army major general and non-resident senior fellow at the Center for European Policy Analysis. NATO's forward land forces, he explains, are multinational battle groups and brigades based in nine countries stretching from Finland to Romania, encompassing the Baltics, Poland, Slovakia and Hungary. Though each has a lead nation, all operate under NATO doctrine that grants them the right to respond in self-defence. They would not need permission to engage. That, however, is only the simplest scenario.

Russia would be expected to prepare for any aggression, and NATO has spent years improving its ability to detect the indicators and warnings that precede hostile intent. Air policing units have already responded kinetically to drone incursions, and an active joint intelligence, surveillance and reconnaissance network monitors air, maritime and land forces across the eastern flank. Any aggression would be preceded by troop movements and the massing of forces, much as was observed along Ukraine's borders in 2021. That build-up prompted NATO to react, with various nations approaching Russia to make clear that its actions looked less like intimidation and more like preparation for an offensive. The same logic applies to the Baltics, where military preparations are constantly observed across the border to gauge Russian intent. Visual signals, radio traffic and satellite imagery all contribute to the picture, and that intent would be explained to senior leadership, including the Supreme Allied Commander Europe and the North Atlantic Council.

NATO commanders can enhance readiness on their own authority. The Allied Reaction Force, which replaced the NATO Reaction Force, can be deployed in whole or in part by SACEUR without waiting for a council decision. That authority, granted after 2022, is significant. If those forces were in place and came under attack, they could respond. But deployment and employment are different matters. If NATO had not yet been attacked, employing forces in hostile action would require a council decision. Once aggression occurs, a nation under attack can invoke Article 5, and other nations may decide to assist without a council decision, as happened in 2014 when the United States sent air and land forces to the Baltics after Russian aggression in Ukraine.

A country under attack would likely invoke Article 5, request assistance and seek either Article 4 consultations or a collective invocation of Article 5. A collective decision carries greater political weight, demonstrating solidarity and allowing NATO to employ its command structure. For clear aggression, such as troops crossing a border or significant strikes into allied territory, the discussion is not whether Article 5 applies but how to respond. Cruise and ballistic missiles, along with mass drone attacks, are increasingly easy to attribute, thanks to expanded air surveillance and border security across the eastern flank. It is unlikely that aggression would be unclear or deniable.

Davis acknowledges the risk of a disjointed response but considers the chance of NATO freezing to be low. His greater concern is the lack of a coherent, timely collective military response. Even without a quick NATO decision, countries with forward-deployed forces, including Canada, Germany, the UK, France, the Baltic states, Sweden, Finland, the US and Poland, would move quickly. They have reinforcement plans that could be enacted within days without a collective decision. Those nations would protect their own soldiers on allied soil, which is precisely why the forces are stationed forward and are larger than ever. The eventual collective response is made more likely by the commitment of major powers to the defence of the eastern flank.

Russia might dispute attribution in hybrid scenarios, such as unmarked drones attacking a German transport, but Davis finds such explanations implausible. The bigger question is the extent of the allied response. Discussions would cover what to strike and how to contain escalation below the nuclear threshold. Striking Russian forces inside Russia would be considered, with the first targets being those used to attack allied soil. Davis describes the logic plainly: you do not simply try to catch all the arrows, you strike the archer. That principle is well understood in NATO defence policy. The alliance would nonetheless restrain itself, likely avoiding anything linked to nuclear capability, including dual-capable aircraft and submarines. Ukraine's strikes on such aircraft and their bases, when not loaded with nuclear weapons, have helped clarify Russian red lines.

Davis dismisses the notion that a country worried about Russian attack would refuse to support a collective invocation of Article 5. It is in every ally's interest to recognise when another is threatened, because it could be their turn next. Nor are allies required to send anything beyond what they have agreed in defence plans. Not all 31 members would need to engage for the response to be significant. Once the major nations commit, others tend to follow. The greater risk, he suggests, lies in future interpretations of Article 5 by far-right governments, such as the AfD in Germany or the National Rally in France. Russian miscalculation is another concern. Allies may respond robustly, striking the forces involved and threatening others elsewhere as a warning. If Russia assumes NATO will hesitate, it may be wrong, opening the possibility of horizontal or vertical escalation. NATO would have to react rapidly and robustly, lacking the integrated missile defence that Ukraine now possesses.

On the likelihood of an attack on the Baltic states, Davis notes that reinforcement of the eastern flank has accelerated month by month. Many see the risk of a limited Russian attack, once low, as growing, on the assumption that Vladimir Putin perceives a window before defences are solid. Davis still considers the risk fairly low. With its war in Ukraine ongoing, Russia could not mount a limited land grab, especially given Ukraine's demonstrated capacity for combined-arms warfare and autonomous systems. Were Russia to take its eye off Ukraine and attack an allied nation, it would struggle to hold ground. Hybrid warfare is far more likely, though Davis is concerned about allied vulnerability to air and missile threats. On a recent visit to Poland, Latvia and Lithuania, he found defence ministries and armies taking the threat seriously, planning capabilities, early warning, obstacles and reinforcement in lockstep with that assessment. They watch constantly and share intelligence. If a potential threat emerged, they would see it.