No, you're right, this is a failing of the whole world, or at least all those that hold any power in it. The answer here is to adapt and mitigate these sorts of outcomes in the future by dropping our current 'us vs them' ideology and replace it with one that looks out for the interests of everyone, understanding that our needs as humans for security and stability are largely universal, and our self-interests need to be tempered.
I agree with all your points, but ironically what you said here is sort of another form of what Mearsheimer seems to advocate- carefully think things through to prevent provocations and escalations, based on a consideration of the concerns and fears of other involved parties.
That being said, while there may be many factors involved leading up to Russia's invasion of Ukraine, it's still Russia invading Ukraine.
If an external party pays the corrupt government of one of the two parties, to genocide their own citizens, that external third party is complicit in war.