Opposing a military invasion that someone else started is not the same thing as starting war after war. Defensive war means that if someone else starts a war by invading another country, then other countries ally to stop it and restore the status quo. If invasions are allowed to continue without opposition, then every would-be conqueror is encouraged and we end up with more war, not less.
All things being equal, you are correct.
But, in my opinion, the current mess in Ukraine is exactly that: One big mess.
All these decades worth of shenanigans in the Ukraine from every player in this debacle begs the question: What does “restore the status quo” in Ukraine really mean?
I don't disagree that it's a mess, but
every war is a big mess. That was true of WWI, WWII, Korea, Vietnam, Kuwait, Afghanistan, etc. For example, the U.S. did a ton of shit in Hawaii prior to the Pearl Harbor attack. But there are still principles that apply. If principles are going to matter at all, then they have to matter in messy real-world cases.
In Ukraine, restoring the status quo means restoring the state prior to the military invasion - i.e. how things were on Feb 23rd. That doesn't mean that all the other shenanigans were OK, but the invasion was definitely *not* OK. Every country should get the message that attempting such an invasion is a huge mistake, and that there is no benefit to doing so. To my mind, that's absolutely vital - and has repercussions far beyond Ukraine itself.
And millions of innocent Ukrainian people are getting screwed while major world powers try to impose their will on the region in the most dangerous war in my lifetime.
I agree that it sucks for the Ukrainians. So what do you suggest is best to do for the Ukrainians right now? I had previously suggested donating to the charity, United Help Ukraine - which is the highest rating in Charity Navigator, has an established reputation, and has transparency about where their money goes.
https://unitedhelpukraine.org/My church is also encouraging donations to the Hungarian Unitarian church which is working to help refugees, but that's Unitarian specific, so I'm not necessarily suggesting that for others.
Beyond individual charities, I dislike token moves that are just for show - but I think economic sanctions that actually have an effect are good - both for Ukrainians and for world peace. Letting invasions succeed and thrive is just asking for more trouble in the future. It is like paying off terrorist demands, which encourages more terrorism.