Article 5 says if you fuck with any NATO nation, it's WW3 time because no one has ever learned a lesson about these kinds of treaties.

It's from the NATO treaty, "Article 5 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."