Answer:
"An attack on one is an attack on all."
Explanation:
The North Atlantic Treaty Organization was established in 1949, and was originally meant to deter the spread of communism stemming from the Soviet Union post-WWII. It was also meant to deter a belligerent nation from starting war with one of the NATO members, since the weight of all those nation's militaries would fall on that belligerent nation.
NATO is currently made up of 30 countries who have joined in varying times of history, with the most prominent member today being the United States.
