NATO has no war code of its own: its forces follow international humanitarian law, and each operation gets rules of engagement agreed by all allies.
What the treaty allows
The North Atlantic Treaty of 1949 sets the outer limits on the use of force.
- Peaceful settlement first. Article 1 commits the allies to settle disputes by peaceful means and to refrain from the threat or use of force “in any manner inconsistent with the purposes of the United Nations.”
- Self-defense in a fixed area. Article 5 covers self-defense against an armed attack on an ally, within the area Article 6 defines, and each ally acts under its own constitution. The details are in What is NATO Article 5?
- The UN comes first. Article 7 says nothing in the treaty affects the Security Council’s primary responsibility for international peace and security.
- Beyond self-defense. For crisis-management missions, NATO’s own doctrine says the legal basis is a UN Security Council resolution under Chapter VII or the invitation or consent of the legitimate government of the country where troops deploy.
The rule has a contested exception. NATO’s 78-day air campaign over Kosovo in 1999 was launched on a North Atlantic Council decision, “to halt the humanitarian catastrophe” there; the Security Council’s resolution on Kosovo came only when the bombing was suspended. International lawyers still disagree about whether the campaign was lawful.
How NATO decides to use force
Every NATO decision, including one to launch an operation, is taken by consensus in the North Atlantic Council. There is no vote; one ally’s objection is enough to stop it. The same rule covers the operation’s rules of engagement, which the Council approves on the advice of NATO’s military authorities. The general framework, a document called MC 362/1 issued in 2003, was unclassified according to NATO’s 2010 legal deskbook; the actual rules for each operation become classified once they are written into its plan.
Rules of engagement translate law and politics into orders: when troops may open fire, against which targets, with which weapons and after what warnings. In the words of NATO doctrine they are “not a comprehensive statement of either the law or policy, although they take account of both”, and they do not limit a soldier’s legal right to self-defense where force is necessary and proportionate.
Who commands the troops
NATO owns almost no forces itself; nearly everything belongs to member states and is lent for a specific mission. When that happens, nations hand NATO commanders operational command or operational control, never full command. They can also attach national caveats, restrictions on what their own units may do, such as where they may deploy or which tasks they may take on. What the alliance does own, and how many troops its members have, is in How many troops does NATO have?
Which laws of war apply
Once force is used, NATO troops are bound by the same international humanitarian law as any army. All 32 allies are party to the four Geneva Conventions of 1949, which protect the wounded, prisoners and civilians. Additional Protocol I of 1977 adds detailed rules on distinguishing civilians from military targets and on proportionate attacks. It has 175 states parties, but not every ally is among them: the United States signed it and never ratified it, and Türkiye has not signed it.
NATO adopted a policy for the protection of civilians in 2016, which states that “all feasible measures must be taken to avoid, minimize and mitigate harm to civilians.”
What NATO cannot do
It cannot order any ally to go to war; each decides its own contribution. It cannot act unless every ally agrees. It cannot conscript soldiers or spend money its members have not given it. The strength of the system is that 32 governments have to agree before anyone moves. Its weakness, against an opponent who decides alone, is speed. The Article 4 page shows how allies consult when threatened, and European defence in numbers shows what Europe contributes.