NATO, or the North Atlantic Treaty Organization, drafted its charter in 1949 and included the principle of “collective self-defense.” The clause was included in Article 5 of the document and has been treated as the cornerstone of the alliance.

NATO was formed nearly four years after the second world war ended and tension between the United States and Russia was spiking. Many European countries flocked to join NATO in order to suppress Russian aggression.

Also Read: War in Ukraine entering ‘protracted phase’, says defence minister to NATO

What does Article 5 say?

According to NATO’s official website, Article 5 of the NATO charter states:

“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 the 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.”

What does this mean?

The principle of collective self-defense means that if any party decides to conduct an armed attack against any member state of NATO, it will be considered an attack against the whole alliance.

In such a situation, the whole of NATO (currently consisting of 30 countries) would be clear to respond to the attack.

Has Article 5 ever been invoked?

The article relating to collective self-defense has only been invoked once in NATO’s decades of existence. After the September 11 attacks in the United States, multiple NATO countries joined America’s response in the Middle East. Allied countries joined the United States in Afghanistan, Iraq and Syria.

During the 2014 annexation of Crimea, NATO allies bolstered forces in Estonia, Latvia, Lithuania and Poland, CNN reported.

Also Read: Why is Turkey opposed to Finland, Sweden joining NATO?

How does Article 5 apply in the current Russia-Ukraine situation?

Ukraine is currently not a member of NATO, even though it once wanted to join the alliance. This means that Russia’s invasion of Ukraine does not trigger the enforcement of the principle of collective self-defense. 

However, many countries in the region are part of the alliance and if the invasion spreads to other member countries, NATO would be cleared to respond.

Tensions have again flared between Russia and western European countries after Finland and Sweden submitted their applications to join NATO. Their admission is expected to be swift.