What is Article 5 in NATO pact and what does it mean for Russia-Ukraine conflict?

NATO has been central to the western response against Russia's invasion of Ukraine since the outset of the war in February.

At the same time, leaders from its member states have been vocal in reaffirming their commitment to Article 5 of NATO's founding treaty.

Since the invasion began, the US and many European nations have looked to NATO for their response and have been vocal in their commitment to the alliance.

NATO (North Atlantic Treaty Organization) is a defensive military alliance of 30 countries, compromising 27 European and two North American nations, as well as Turkey.

In recent months, a number of NATO members have undertaken missions to deploy greater numbers of troops to nearby countries of Ukraine.

For example, US President Joe Biden said America would deploy 7,000 more soldiers to Germany to bolster Europe's defences.

In addition, the UK and Germany said they would send more of their forces to the Baltic States and Poland via NATO.

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NATO has also activated special defence plans to give commanders in eastern Europe more freedom to react to the situation and deploy forces if needed.

All of this has been done with reference to Article 5, yet no troops have been sent into Ukraine.

More recently, the deaths of two people due to a missile which landed within Poland, near to its border with Ukraine, has sparked debate once more as to whether Article 5 should be triggered.

But what exactly does Article 5 require of NATO members?

What is Article 5?

NATO was founded in 1949 when the US, the UK, Portugal, Norway, Netherlands, Luxembourg, Belgium, Italy, France, Iceland, Denmark and Canada signed the North Atlantic Treaty in Washington DC.

The alliance is defensive in nature and is not supposed to orchestrate offensive operations.

Central to the treaty is Article 5, which enshrined the principle of collective defence. In short, this means an attack against one ally is considered an attack against all allies.

Article 5 was invoked for the first time in the wake of 9/11, obliging all member states to come to the US's aid.

As a consequence, a large global coalition was formed, which led to the invasion of Afghanistan in 2001.

Although Ukraine has several agreements with NATO and aspires to join the alliance one day, the country is not a member and so is not protected by Article 5.

Consequently, this is one of the reasons why western forces have not been deployed to defend Ukraine.

However, because of Russia's unprecedented aggression, NATO nations like Romania, Poland and the Baltics (all former Soviet states) have indicated they feel increasingly threatened by Moscow.

As a result, the US has been deploying troops across Europe, in order to remind Russia it will not tolerate any invasion of a NATO nation and to reassure its allies.

President Biden has also been keen to emphasise his commitment to the alliance after his predecessor, Donald Trump, spent years criticising it and expressing reluctance to defend Europe.

At one stage, European nations felt so threatened that shortly after Russia's invasion began, Bulgaria, the Czech Republic, Estonia, Latvia, Lithuania, Poland, Romania and Slovakia all collectively triggered Article 4 of the treaty.

Article 4 allows nations to call for urgent consultations when "the territorial integrity, political independence or security of any of the parties is threatened".

It was only the sixth time it has been triggered, and never before was it triggered by so many nations at the same time.