Article 5 is the most well-known part of the Nato treaty.
If it’s invoked, members will take ‘action it deems necessary’ to ‘restore and maintain the security’ of the North Atlantic – which could include the used of armed forces.
Essentially, an attack on one member is an attack on all.
It has only been invoked once in its history.
On September 12, 2001, a day after the Al Qaeda terrorist attacks in New York and Washington DC, members triggered it, meaning Nato members would support the US’s response to the attacks.
Article 4 has been invoked on numerous occasions.
It is launched if a member is concerned for its safety,marking the start of formal emergency consultations.
It was triggered by Turkey in 2002 after the conflict in Iraq and was jointly invoked by Bulgaria, Czechia, Estonia, Latvia, Lithuania, Poland, Romania and Slovakia after the Russian invasion of Ukraine.
