That was in the early 90s.
From 1999 to 2004 countries joined for fear of Russian revanchism.
Article 5 was invoked just once in NATO history - on the day after 9/11
You might want to bone up on your history. The NATO military campaign against Serbia was in 1999. The NATO military campaign in Libya was in
2011. Interestingly, both of these absolutely reinforced any seemingly outlandish claims on the part of the Russian government that NATO is a coalition of governments with predatory intentions, not a treaty organization that serves a defensive purpose.
Article 5 was invoked just once in NATO history - on the day after 9/11.
This also contradicts your prior assertion about NATO serving to protect Europe from Russian aggression, doesn't it?