After the September 11 attacks, NATO invoked Article 5 of its treaty which stated that allied nations must support
a. a nation under attack.
c. a nation attacking another nation.
b. a nation in war.
d. any nation in the treaty for any reason.
Article 5 of the NATO treaty states that allied nations must support "d. any nation in the treaty for any reason," since it says that a nation in the treaty under attack means that all the nations in the treaty are under attack.
