Article five
An attack on one member of our alliance is an attack on all of them.
Article 5 is at the basis of a fundamental principle of the North Atlantic Treaty Organisation.
As you all probably know it provides that if a NATO Ally is the victim of an armed attack, each and every other member of the Alliance will consider this act of violence as an armed attack against all members and will take the actions it deems necessary to assist the Ally attacked.
This is the principle of collective defence.
Respect to their fallen