From my reading it appears to me that NATO has never initiated a war but only reacted to conflicts already happening? Is this interpretation correct? I find it important to answer as many pro-russian sources claim NATO to be an aggressor, but I have the complete opposite impression.
The list of NATO operations (List of NATO operations) indicates that NATO never started a war but only intervened.
Also List of wars 1945-1989 does not indicate that NATO has ever started a war.
I'm not interested if members of NATO have started wars themself (e.g. US did) but if starting a war was ever part of a NATO mission.
Since many comments are about what consists starting a war. I would suggest to define starting a war as the party which physically escalates first.
Following the definition of war by Oxford dictionary:
"a situation in which two or more countries or groups of people fight against each other over a period of time."