Well duh, it’s a defensive alliance.

Tell that to the people of yugoslavia in 1999

Or Bosnia in 95

Nato intervened when Serbian forces committed genocide against the Bosnians.
en.wikipedia.org/wiki/Bosnian_War

the July 1995 Srebrenica massacre later became iconic of the conflict. The massacre of over 8,000 Bosniak males by Serb forces

That’s when NATO decided to intervene.