There are only two routes out of this: Persuade Russia to stop, or persuade Ukraine to stop. To persuade Russia to stop, you have to persuade Putin to stop. But Putin won't, not with anything short of victory as perceived by him (or at least something he can sell to his people as victory). And Ukraine won't, not without their territory back. There is no common ground between them.
That leaves the options as either assassinate Putin, or intervene strongly enough so that one side or the other receives irrevocable military defeat. So, concretely, what exactly do you think the world should have done??
Americans need to stop thinking that leaders act alone and everyone under them only accepts orders.
Nothing will change because those currently enjoying their privilege because of their position dont want that to change. If it kills millions of others, they simply dont care. It doesnt bother the current batch of generals to send thousnads to die on a daily basis why would that change tomorrow if Putin dies ?
If Putin dies tomorrow, those generals have a decision to make: Do they want to continue fighting on the front lines in Ukraine, and maybe get killed? Or do they want to rush back into the power vacuum created by Putin's death, and see if they can be the one (or one of the ones) that emerges with power?
It is about giving up territory AND being attacked again.
What would be the point of that?