I'm not entirely sure that that is the case and Germany was the primary reason for NATO forming. It surely was meant to hinder the spread of communism/Soviets.

And yes, a defense alliance can be flexible and change its objectives with the times, that's not counter to the point I was making. I'm not sure how to better express myself, I really think it is obvious that a defense alliance must be defending its members from _external_ threats.

If there is no possible threat (real or perceived, present or future) then no alliance is formed. That is the whole purpose, _the definition_ of a defense alliance.

I don't know how to express this notion with more clarity.