There are four main NATO "operations" that can be interpreted as starting a war:
Bosnian War. NATO intervened with Operation Deliberate Force.
Kosovo War. NATO intervened with Operation Allied Force.
2011 military intervention in Libya. NATO intervened to impose a no-fly zone.
War in Afghanistan...
Indeed. Just like one side's terrorist is another side's freedom fighter, so is an operation which one side considers an "invasion" is another side's "peacekeeping operation".
Kosovo conflict was a low level insurgency before the intervention. NATO escalated it to a full-blown war encompassing the entire territory of Serbia. Somewhat analogous to a low-level Donbass conflict and the massive Russian invasion of the entire country.
How can you argue that Bosnian or Kosovo wars were started by NATO? As your own answer states, those wars were already ongoing... thus NATO didn't start them. I think this answer really needs the first two bullet points removed... arguably the third, too.
@vsz Likewise, who started any war depends on exactly where the line is between political antagonism and war. And you can define that line to make either side the aggressor.
Re the claim there was a civil war in Libya before NATO intervened (19 Mar). Who funded and coordinated the anti-Gaddafi opposition (TNC) in 1/2011? The First Libyan Civil War was 15 Feb-23 Oct 2011. By Jun 2011, Italy, France, Kuwait, were openly funding the TNC for ~$1bn, also the US allowed the TNC access to $30bn in frozen assets. But even back in 3/2011, Obama authorized secret help for Libya rebels
...seems more correct merely to state "It is not publicly confirmed that NATO member states were officially funding the opposition before mid-March" Re the Timeline: 15 Feb, the Benghazi protests began. 22 Feb, Libya's UN diplomats broke with Gaddafi. 26 Feb, UNSC Resolution. Pressure mounts for no-fly zone. 10 Mar: French PM Sarkozy meets Libyan NTC in Paris, recognizes as legitimate govt. 17 Mar UNSC RES 1973 (no-fly zone). 19 Mar French air intervention in Benghazi. 21 Mar: Obama invokes War Powers Resolution ...
...it really seems implausible hairsplitting to claim that there was no covert foreign funding, coordination or assistance by any NATO member before NATO finally "officially" got involved 19 Mar, and that a grassroots domestic opposition had spontaneously sprung up 1/2011 all by itself. Also spontaneously happened at the exact same time next door in Egypt, Yemen, Syria, and Bahrain. What a coincidence.
@TylerH there's where things get fuzzy. If the Kosovo war was a low-level conflict before NATO's intervention, and therefore NATO didn't start it, then you could argue that the Donbass conflict was a low-level conflict before Russia invaded and therefore Russia didn't start the current war. Similarly, if you argue that NATO didn't start the war in Libya (see smci's comment) then someone else could argue that NATO started the second Libyan Civil War, which would never have happened if Gaddafi remained in power. It really depends on your definition, and different people can disagree.
Deliberate Force had a UN mandate. Allied Force did not, but the war was already ongoing. The only time NATO started a war was in Afghanistan -- a decision that is still quite controversial.
The invasion of Afghanistan was not a NATO operation. Although NATO later became officially involved, the initial invasion was the US and the UK acting on their own.
@Allure You could, except isn't the international community in agreement that the Donbass conflict was started by Russian plants who infiltrated Ukraine to foment said conflict in the first place (I did not follow that conflict so don't know, but that's what I had thought was the case). I do consider hostile covert actions to be tantamount to acts of war too, if we're considering the argument "who started it" (and yes that means the US and Russia have started most of the wars in the last 75 years, probably).
Discussion on answer by Allure: Has N…
Discussion on answer by Allure: Has N…