Most likely sanctions.

If NATO and the US directly intervene Putin may go nuclear. Then everybody dies.

Putin is going to push his luck as far as he can. Ukraine is just the start, first item on the list.

The best the rest of the world can do is hope the sanctions and the financial stranglehold will be enough to bring this to an end. But that’s really hoping with all my hope in my heart of hearts.

If the world does intervene and Putin decides to declare a nuclear strike then the best hope the entire world has is counting on someone in his inner circle to remove Putin. Those who surround Putin are the ones who could save the world, I hope they realize it and don’t let him launch a nuke.

Once the first nuke is sent, the entire stockpile is being launched on all sides.