NATO Article 5 is misunderstood - an attack on a treaty member does NOT mean other members have to defend them.

[Knajjd]

I read everywhere that if a member of NATO is attacked all others members will defend it but that's not the case. Other members can do nothing if they so decide.

Here is an extract from the Wiki page on Article 5:

The key section of the treaty is Article 5. Its commitment clause defines the casus foederis. It commits each member state to consider an armed attack against one member state, in the areas defined by Article 6, to be an armed attack against them all. Upon such attack, each member state is to assist by taking "such action as [the member state] deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."

Source:

North Atlantic Treaty - Wikipedia

en.wikipedia.org

 

[The Notorious SLAV]

Technically speaking it doesn't, but in real life situations, 99% of the time it would end so. It's very hard to imagine a scenario where a NATO member would be attacked but the other members would not step in, while not fearing that doing so would be a show of weakness or impotence, or threaten the alliance's overall strength. Maybe if the US was attacked by someone the others could sit it out since it sure doesn't need any other country to defeat its enemies, but the others are reliant on NATO and so an immediate and widespread reaction to any threat to any member is in their interest, lest the alliance risk getting weaker.