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What If Putin Attacks NATO? Here Is What Could Happen Next

A Challenger 2 Main Battle Tank of the Royal Welsh Battle Group on Exercise Prairie Storm at the British Army Training Unit Suffield (BATUS) in Canada. The prairie of Alberta has provided an excellent opportunity for the British Army to train on a large scale since 1972. The British Army Training Unit Suffield (BATUS) is an organisation situated on one of the most sparsely populated areas of the Alberta plain. BATUS is equipped with in excess of 1000 vehicles including a full complement of Challenger 2 tanks and Warrior Infantry Fighting Vehicles. Each year a Regiment is sent there for six months to take the part of the 'enemy' for the other Regiments that are there to train each year.

Would NATO go to war? What are the United States’ legal obligations if Russian President Vladimir Putin orders his military to invade a NATO country and NATO invokes Article 5 of the treaty, the collective self-defense provision?

The answer to this legal question, which is complicated, is the narrow focus on this article. Before diving in, however, it’s important to start with a few caveats.

First, as my colleagues have already written (see hereherehere and here), Putin’s invasion of Ukraine, a non-NATO country, has been unlawful, despicable, and totally unwarranted. Ukrainian President Volodymyr Zelenskyy, a former actor and comedian before running for office, has been nothing short of inspiring, brave, and patriotic, as have the people of Ukraine.

At this point in time, given the Russian military’s lackluster and uncoordinated military assault across the country, and the stiff resistance by the Ukrainian military and civilian population, it’s an open question of whether Russia will succeed in its military objective. But given the sheer size of the Russian military, its willingness to unlawfully target civilians and carry out other actions arguably in violation of the law of war and the Geneva Conventions, it may, over time, succeed.

Second, the answer to the legal question posed above does not—and is not intended to—answer the following very important questions: If a NATO country is invaded, do we have a moral obligation to send American forces in harm’s way? Would it be in our nation’s interest to send American forces? Would sending American forces, or providing other military, intelligence, or logistical assistance, increase the chances of a world war?

The narrow focus of this article is solely on delineating our legal obligations.

Third, sprinkled throughout the Q&A below are hyperlinks to previous opinions by the Office of Legal Counsel in the Justice Department across several administrations. No doubt, if, God forbid, Putin was successful in Ukraine and decided to invade a NATO country, administration lawyers and scholars in the law of war would turn to these (and related) Office of Legal Counsel opinions for guidance. As such, we have a fairly good starting point.

Fourth, this is a complicated issue. This article is not meant to be a comprehensive explanation or analysis of our domestic or international legal obligations. Rather, it should be read as merely a starting point for those interested in delving more deeply into the issues, should this scenario come to pass. Let’s hope and pray they do not.

QUESTION: What is the North Atlantic Treaty Organization?

ANSWER: The North Atlantic Treaty Organization, as stated on the State Department website, was created in 1949 by the United States, Canada, and several Western European nations to provide collective security against the then-Soviet Union. It was the first peacetime military alliance the United States entered into outside of the Western Hemisphere.

QUESTION: What is the North Atlantic Treaty?

ANSWER: A series of events in Europe between 1947 and 1948 caused the nations of Western Europe to become concerned about their physical and political security and caused the United States to become more closely involved in European affairs.

Great Britain, France, the Netherlands, and Luxembourg signed the Brussels Treaty in March 1948, which provided that if any one of their countries was attacked, the others were required to help defend it. Two months later, Sen. Arthur Vandenberg proposed a resolution that President Harry Truman seek a security treaty with Europe.

When that resolution passed, negotiations began for the North Atlantic Treaty. European nations wanted assurances that the United States would intervene automatically in the event of an attack on a member country.

But as I have written elsewhere, the power to declare war (Article I, Section 8, Clause 11 of the Constitution) rests with Congress alone, so they worked out language (see below) that respected our constitutional framework.

QUESTION: What countries are members of NATO today?

ANSWER: As of today, there are 30 NATO countries, including the United States, the United Kingdom, France, Germany, Italy, Poland, Spain, and others (found here).

QUESTION: What does Article 5 say?

ANSWER: The text of Article 5 of the treaty is:

The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defense recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.

Any such armed attack and all measures taken as a result thereof shall immediately be reported to the Security Council. Such measures shall be terminated when the Security Council has taken the measures necessary to restore and maintain international peace and security.

QUESTION: Why is Article 11 of the treaty important?

ANSWER: The text of Article 11 reads:

This Treaty shall be ratified and its provisions carried out by the Parties in accordance with their respective constitutional processes. The instruments of ratification shall be deposited as soon as possible with the Government of the United States of America, which will notify all the other signatories of each deposit.

The Treaty shall enter into force between the States which have ratified it as soon as the ratifications of the majority of the signatories, including the ratifications of Belgium, Canada, France, Luxembourg, the Netherlands, the United Kingdom and the United States, have been deposited and shall come into effect with respect to other States on the date of the deposit of their ratifications.

The key language to focus on, from a legal perspective, is “in accordance with their respective constitutional processes.” That is the compromise language hammered out by the United States delegation and Western European countries.

This recognizes the fact that only Congress can declare war or pass an Authorization for the Use of Military Force, which I have written about in a different context here.

QUESTION: In deciding whether to order the armed forces of the United States into harm’s way, are there threshold questions to answer?

ANSWER: Yes. There are two: (1) Is it in the national security interests of the United States to do so, and (2) Do the actions of the party (in this case, Russia) amount to an “armed attack” as defined by Article 51 of the U.N. charter?

QUESTION: Does an attack on a NATO ally require—as a matter of international law—the United States to respond with force?

ANSWER: No. We would never agree to that. As one law of war expert recently explained to me, from a policy perspective, it has been important to convey the impression that we would respond to an armed attack on a NATO ally with military force.

However, Article 5 permits the United States to respond in a way that satisfies its legal obligations short of sending in the armed forces of the United States to fight, such as providing military equipment or other aid.

QUESTION: If a U.S. president wants to respond militarily to an attack on a NATO ally, does he have the unilateral authority to do so?

ANSWER: The answer depends on where you stand, as a legal matter, on a president’s unilateral authority to use force.

Here, there are several Office of Legal Counsel opinions to consider, depending on your view on the president’s inherent authority under Article II as the commander in chief. Each Office of Legal Counsel opinion is fact-dependent.

For example, one such opinion from Oct. 23, 2002, regarding the use of force against Iraq, is extremely broad. Written by Jay Bybee, then-assistant attorney general for the Office of Legal Counsel, the relevant part of the 48-page memo reads:

Accordingly, we believe that the President’s constitutional authority to undertake military action to protect the national security interests of the United States is firmly established in the text and structure of the Constitution and in executive branch practice.

Thus, to the extent that the President were to determine that military action against Iraq would protect our national interests, he could take such action based on his independent constitutional authority; no action by Congress would be necessary.

For example, were the President to conclude that Iraq’s development of [weapons of mass destruction] might endanger our national security because of the risk that such weapons either would be targeted against the United States, or would be used to destabilize the region, he could direct the use of military force against Iraq to destroy its WMD capability.

Or were it the President’s judgment that a change of regime in Iraq would remove a threat to our national interests, he could direct the use of force to achieve that goal.  Were the President to take such action, he would be acting consistent with the historical practice of the executive branch.

Another broad, but not as broad, Office of Legal Counsel opinion that also concluded that the president could use force unilaterally (i.e., with express authorization from Congress) can be found in this 2018 Syria opinion by Steve Engel.

This 2011 Office of Legal Counsel opinion regarding the unilateral use of force in Libya by Caroline Krass concludes that the “[p]resident has the constitutional authority to direct the use of force in Libya because he could reasonably determine that such use of force was in the national interest. We also advised that prior congressional approval was not constitutionally required to use military force in the limited operations under consideration.”

There are a handful of other Office of Legal Counsel opinions that will be instructive to lawyers in the executive branch should this issue arise. Examples include:

speech by Defense Department General Counsel Paul Ney on the domestic and international law basis for the 2020 airstrike that killed Qassem Soleimani is also useful to the analysis.

QUESTION: If Putin invades a NATO country and triggers Article 5, and the president finds that it is in the nation’s national security interest to respond militarily and such actions rise to the level of war, should President Joe Biden seek congressional authorization for the use of military force or, alternatively, seek a declaration of war under Article I, Section 8, Clause 11?

ANSWER: This is a policy question, not a legal question.

All countries enjoy the inherent right of self-defense. It would be impractical for the president of the United States to seek congressional authorization for the use of military force in an emergency situation. But sending the armed forces of the United States abroad to defend a NATO ally that is attacked by Russia would likely not be considered an emergency situation.

For those interested in reading more about the genesis of Article 5, the North Atlantic Treaty, and related law of war concepts, read this 2019 law review article by professor Michael Schmitt.

Charles “Cully” Stimson is a leading expert in national security, homeland security, crime control, immigration, and drug policy at The Heritage Foundation’s Center for Legal and Judicial Studies. 

Written By

Charles “Cully” Stimson is a widely recognized policy expert in crime control, national security, immigration, homeland security, and drug policy at The Heritage Foundation. Stimson is Deputy Director of the Edwin Meese III Center for Legal and Judicial Studies, Manager of the National Security Law Program, and a Senior Legal Fellow. He has also served as the Chief of Staff at Heritage three times and ran the transition for three Heritage presidential changes of command.



  1. Alex

    March 12, 2022 at 2:49 am

    1. It is illegal, shameful and unreasonable to do it like the West, namely to turn a blind eye to the killings, torture and abuse of Ukrainians in the Donbass for 8 years. The offensive of Russia and the militias is not “sluggish and uncoordinated”, but merciful, because the Bandera Nazis hide behind people as a human shield, and this is a terrorist tactic. If Russia had used the scorched earth tactics, everything would have been over long ago, but there their Slav brothers, incl. Russians and Russia can’t do that.
    2. 2. NATO will not intervene for the reason that Russia’s military doctrine says: “in case of aggression, strike at decision-making centers.” Where are these centers? That’s right – Brussels and Washington (and London there too). This means that Russia will not care about attackers the way it cares about Russians and Ukrainians.
    3. Before writing nonsense about invading NATO countries, I advise you to listen to Putin’s address to the Russians at the end of February. It clearly states that a special military operation is being carried out to demilitarize and denazify Ukraine. The West turned a blind eye to the genocide of Ukrainians in eastern Ukraine for 8 years. The Minsk agreements were not implemented, and in the end, the president of Ukraine said: “I don’t like the Minsk agreements,” then the government of Ukraine stated that if they attack the Donbass and Russia intervenes, then Ukrainian missiles will fly to Russian nuclear power plants. And, finally, they announced the beginning of the creation of a dirty nuclear bomb. Few? Further, NATO decided to place its weapons on the territory of Ukraine. Further, American biological laboratories were discovered on the territory of Ukraine with dangerous biological weapons. Few? And Russia is bad. Look after yourself better.
    4. I understand that the article is not intended for explanations, it is intended to create panic among Westerners and statements:
    a) Russia is bad,
    b) If NATO attacks first, it is for the sake of peace.
    Such propaganda is not new, but in the 30-40s. last century worked.

    • Steve

      July 9, 2022 at 8:35 pm

      Seriously, man… Look in the mirror, spit out your Nazi BS, and tell me you don’t look and sound like the crazed Nazi that doesn’t even exist – Get a clue, the invasion has NOTHING to do with Nazis. My gosh, are you really THAT stupid?

      Jesus… Propaganda, no matter how ridiculous, always seems to get to the heartstrings of the most ignorant of humans,

  2. John E. Osman 3rd Veteran of West Berlin

    April 8, 2022 at 6:44 am

    1st off, my commentary is my opinion, & mine only, …

    You state that Russia’s intent, is to “denazify” the country of Ukraine, … which means that Putin wants to get rid of any who would oppose Russian rulings, … and that they will insist by force, for Ukraine to do so, …

    Hmm, that sure sounds very Hitlerish, of scrutinizing the fact that Ukraine is a nation under its own control, & not burdened by what anyone else’s opinion of how they operate their nation, for, by & of themselves, … just kinda like Hitler, when he was polarizing all of the woes of Germany’s 1st WW, upon the Jewish populations of each, & every country that the 3rd Reich, occupied, by force, …
    If they wish to join, NATO, or any other form of governmental action of protecting themselves, then that should be settled by their own Ukrainian governmental bodies, … not Russia, or China, or Iran, anyone else, … period, …

    You make it sound as if the Ukrainian peoples begged Putin to take over the running of the Ukrainian peoples government, …

    I find that not only difficult to believe, but about as farcical, as a cartoon, of a parent, threatening a 20 year old, with corporal punishment, if they stayed out a few hours too late, … it simply will not happen, and the overly parental shadowed youngster, of adult age, will simply find someplace else to live, … and there is no legal precedence, to stop them, … because at the age of 18, most young adults can be drafted, & sent into the military, and have even had 17 year olds enter into the military at 17, … (with parental permission), …

    And were I physically able to be there, I would volunteer, to stand against such evil intentions, …
    I believe it all boils down to this, … Putin, is an old man, who wishes to restore the power, & authority of the USSR, because he was humiliated, when the Soviet Empire, went broke, from their failings to take care of those they controlled, … food was a huge shortage, & it takes a whole of it to feed a series of displaced armies that were spread as thick as jam, on a pbj sandwich, … spread from the North Sea of the Atlantic, to the Aegean Sea, south to Greece, … & that was just their western borders, … they still had to cover their eastern seaboard on the Pacific side of their nation, … and the steel trap, of their governmental over reach was quite exorbitant, … supplying the KGB, with everything they needed to gain influence throughout the global political circles, … places like Freedom Bridge, & the Brandenburger Tor, along with other sites in West Berlin, being one of so many, …
    Bet you did not know, that Putin was a Major, in the KGB, & stationed there in 1974, same exact time frame I was there, … my room mate had found a way into East Berlin, without going through any checkpoints, … he was caught, when he went right after a trip,I had gone on him with only about 2 weeks before, … and was whisked out of West Berlin, only a couple of hours after he was caught, & detained by our side, … it was the very same time I found out about the cache caverns that were to house the people of Berlin from the steady rain of bombing sorties the Allies were pounding the German Reich with, …

    Being there, for 13 months, was enough for me to see, & understand why I was there, … an American soldier, after spending the previous 17 months in West Germany, … where I could not, for the life of me, understand why America, was still in West Germany, after so long, of post WW2, …
    Being in West Berlin, opened my eyes to many political, and strategic issues that made a difference, in those who lived, worked, schooled, and made their homes in West Berlin, … the economics of the world revolves around the corporations, of these huge cities, & that there has been so much conflict over these lands that each street has a history, of its past, that can be delineated by virtue of stories, good, & bad, over the past 1,000 years, … which, in the end has decided on Freedom, for its peoples, over the evil criminal content of other regimes, …

  3. DarylS

    April 12, 2022 at 2:19 am

    In response to Alex. I have read a translation of several of Putin’s speeches, and am puzzled by the contradictions. He talks about deNAZIfying Ukraine, and how these NAZIs are supported by Zionists, Western Liberals, and genderists.
    These groups were slaughtered by the millions by the NAZIs so why would they seek to re-establish them?
    Speaking from the other side of the world I cannot see any justification for a nation to invade another sovereign nation, just because they don’t like that nation’s internal politics. Claiming it was to defend Ukrainian citizens from their own government, omits to mention that these people were in armed revolt against that government.

  4. William Fraser

    April 30, 2022 at 11:34 am

    The Heritage Foundation is a pro MAGA, sedition supporting right wing extremist organization and a disgrace . This article is creepy as is the author.

    • Ray GROSS

      May 12, 2022 at 11:19 am

      The Heritage Foundation is SCARY because they would sacrifice democracy for FASCISM in a New York Minute if it meant They would be the HEAD FASCIST IN CHARGE.
      trump would have bent to Pootins Will and pulled America Out of NATO if he had won in 2020. In every Foreign Policy decision, trump did EXACTLY what benefited POOTIN including the Disgusting Betrayal of our Kurdish Allies and creating dissension with our NATO Allies.
      As China emerges as the Next World Super Power a Strong and Unified NATO becomes More a necessity for America. We should be EAGER to Respond to ANY NATO Ally if Article 5 is triggered.

      • Roger W Oakes

        June 9, 2022 at 8:14 pm

        Ray, Trump and not Obama sent lethal military aid to Ukraine and that certainly was not to Putin’s liking. Trump scolded and threatened NATO allies because they were ripping off the USA as the USA provides WELL OVER 50% of NATO forces and costs while only SOME of the NATO allies spend 2% of their own GDP on their own military forces so as to be able to contribute to NATO defense. THAT was NOT on PUTIN’s want list as STRENGTHENing NATO is not what PUTIN wants. PUTIN respected Trump and knew he was no coward like Biden and Obama who marshall words and speeches and “red lines” as if their lawyer talk has effective ranges like artillery and missiles have ranges. Third, TRUMP destroyed ISIL and that was not to Putin’s favor because it stabilised the region somewhat and only TEMPorarily did he mistakenly agree to terms that hurt the Kurds and helped the NATO ally Turkey. He reversed and stopped this action as it was a mistake that was quickly corrected. Putin LOVED the Biden win in 2020 as he knew he was stronger willed than the Obama/Biden policies and actions. He invaded and took Crimea while Obama did nothing and started the whole war in 2014 while claiming that the Ukrainian Maidain was a US CIA operation and not the ouster of his ally Yanukoyvich from the Ukrainian presidency because he broke his promise to join the European market instead of signing the Russian open market initiative as Putin wanted. The fact that Putin saved him by helicopter is proof enough of that Ukrainian traitor. If Biden had any backbone he would eagerly supply any and all weapons the Ukrainians need to defend themselves and not slow walk them and use terms such as “defensive weapons only” and restrict their usage in a gradual and piecemeal fashion because he is afraid of Putin and nuclear weapons. Trump os not afraid of Putin and knows and understands Putin is a corrupt autocrat who runs circles around the Obama/Biden political teams. These statements are then twisted to paint Trump as a Putin whipping Boy when it is the other way around, as it was the weak Dems who allowed the start of war in 2014 and the loss of Crimea.

    • Steve

      July 9, 2022 at 8:45 pm

      WTF are you babbling about? Pro-Maga? right wing extremist organization? A creepy article.
      Clearly you are a democrat looking for some way to change the fact that the creep in the White House has the blood of 750,000 American Covid casualties, thousands of Afghanis, and tens of thousands of Ukrainians all over him.
      Biden didn’t stand up to Russia to avoid this war, after 4 years of hate-filled Russia Russia Russia! You better believe Russia Collusion is real, you’re lookin’ at it trippin’ and fallin’ all over the White House lawn. So if you wanna bitch about MAGA, first have a clue as to the difference between MAGA and the DNC – One is pro-American; the other is pro-everything else.

  5. Ghengis

    September 5, 2022 at 8:06 am

    Russia needs to be confronted by NATO now and be crushed as it deserves to be for all the evil atrocities it committed in Syria and Ukraine. These Russian Terroists are black hearted bastards, Cowards Yellow streaks run through every Russians Spine,and the are repulsive offensive to look at Eurasian inbred SCUM. Isolate the savage scum for eternity or for just as long for the West can procure a bomb of Types that can incinerate the shit hole country Russia and all the Scum there in with out hurting neighbours.

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