I don't get your question "who can stop them?" The Ukrainians have already done so, to a large degree. Nobody imagined Ukraine lasting more than a week of invasion, but they did so, and then retook large swathes of territory and forced the Russians into a defensive posture.
The mistake the west made was not having confidence in the Ukrainians early on, and not supplying them with the tools early on and into last winter. We let Russia pull back and build intensive defensive lines that would be impossible to breach without air support.
As for nuclear weapons... they are not tools to win wars.
The first country to use a nuclear weapon as an offensive weapon will be turned to glass. It's just not a tool that even Putin is stupid enough to use.
They don't make you a powerful offensive power, just a powerful defensive one. And nobody has ever suggested invading Russia, despite their paranoid claims to the contrary.
The mistake the west made was not having confidence in the Ukrainians early on, and not supplying them with the tools early on and into last winter. We let Russia pull back and build intensive defensive lines that would be impossible to breach without air support.
As for nuclear weapons... they are not tools to win wars.
The first country to use a nuclear weapon as an offensive weapon will be turned to glass. It's just not a tool that even Putin is stupid enough to use.
They don't make you a powerful offensive power, just a powerful defensive one. And nobody has ever suggested invading Russia, despite their paranoid claims to the contrary.