Extend NATO membership to more countries and get them on if they want to in less than a month.

Bring Iran back into the world economy, get them away from Russia. Use them for energy, etc.

Deploy iron dome across eastern europe.

Get a UN-led referendum in various natural localities of Ukraine to decide if they want to be a part of Russia or not. Anywhere that isn't, get them to join NATO. Anywhere that is, well, let people decide which govt they want to belong to.

Playing devil's advocate, are you sure that strangle a nuclear-powered country with vast resources and possibly pushing them into form a coalition with other countries will be a good idea? This will further polarize the world and resentment will run deep after some years. Heck, This looks really similar to the origin story of Hitler just with nuclear bombs as blitzkrieg.

USA withdraw from NATO. Europe can afford to pay for their own defense. My family in USA should not be obliged to pay for it anymore.