What strange times we live in.
In the past, you went to war. Nowadays with nukes at the ready, war = global annihilation.
So... what do we do? Someone like Putin can't be reasoned with. He will only respond to force. But force could lead to human extinction. Putin know this, which is why he's doing what he's doing. The Ukraine isn't the breaking point. China taking Taiwan isn't the breaking point. But what is? Surely there's a breaking point somewhere?
Say Europe or USA fights back with drones and bombs. Russia responds with drones and bombs. So what next, a gentleman's war where we fight and kill each other but with a handshake deal that we won't use nukes? And when one side is about to lose, they just surrender instead of firing?
This is a testament to how fragile a global society really is. Society functions on a bunch of imagined realities. Money has value, human beings have certain rights, laws, borders... these are all just imagined realities. If tomorrow we all decided not to accept them anymore, they'd just be gone. Nothing actually tethers them to reality.
So here we were, sharing the imagined reality that "no one would do something like this because of the threat of nuclear warfare" and Putin just said "meh, fuck it". So now what? That particular imagined reality is shattered.