1. The most straightforward way would be for Russia and Ukraine to have implemented the Minsk II Agreements at any time since 2015, when they were introduced. Minsk II says as soon as the Donbas region gets some autonomy and votes for their own representatives, Ukraine would get control over the entire borders of its country, everyone would get amnesty, lay down their arms, and unicorns would frolic around. But for some reason this was considered "bad" and the election kept being postponed:
https://en.wikipedia.org/wiki/Minsk_agreements#Evaluation_an...
As a libertarian, I blame the politicians: https://www.youtube.com/watch?v=Mg4Jmnw3xQg
2. An easy way that the USA could unilaterally prevent this escalation is simply to say that Ukraine would not join NATO. Tulsi Gabbard for instance literally said this in the first days of the war: https://www.youtube.com/watch?v=OF5oPNjMZw4
Until 2009, most of Ukraine was against joining NATO: https://www.kyivpost.com/post/10444
But George W Bush, besides invading Iraq, also for some reason insisted, demanded that Ukraine and Georgia join NATO anyway: https://www.reuters.com/article/us-nato-ukraine-bush/bush-vo...
The following presidents could have simply rolled this back. Not even other NATO countries really wanted what George W Bush was pushing, but it turned into an escalation.
And literally every responsible person was warning about this for decades: https://theconversation.com/ukraine-war-follows-decades-of-w...
https://www.armscontrol.org/act/1997-06/arms-control-today/o...
The problem is these people were just ignored by the decision makers in power: https://www.youtube.com/watch?app=desktop&v=KqE7UTptgGg
I wouldn't say it's "unprovoked". It was not provoked by Ukraine, but certainly by NATO's expansion. A lot of people around the world feel this way, including leaders of billions of people (China, India, the catholic Pope, etc.) https://www.youtube.com/watch?v=oEbVBi1f0e8 and the people themselves
India: https://thewire.in/world/more-indians-hold-us-nato-responsib...
China: https://uscnpm.org/2022/04/19/chinese-public-opinion-war-in-...
3. To be 100% clear, the CIVILIANS of any country are not to blame for any of this. The people of Ukraine are victims in this, just like Iraqis were victims of US invasion and occupation. But I can still blame Saddam Hussein for ousting inspectors and giving the US an excuse to invade. If you think the Russian invasion was "unprovoked", then the invasion on Iraq was even more unprovoked. But both are far more provoked than, say, the US bombing of Laos to the stone age, more than any country has ever been bombed in history. Totally unprovoked "special military operation", completely. There have to be ways to stop this. And it's called respect for human life and having public discussions with leaders instead of bombing their population.
Just my 2 cents.