[Sawdring]

An attack on NATO is an attack on its allies.

[johniegrad]

An attack on NATO is an attack on its allies.

Until it’s not.

[Lonesome in Massachussets]

An attack on NATO is an attack on its allies.

Not an attack on an extraterritorial expeditionary force. Afghanistan harbored the organization responsible for 9/11 and the U.S. invoked Article 5 ("An attack on one is an attack on all.") 9/11 was an attack on U.S. soil.