As horrific and needless violence unfolds in Ukraine, my friends, family, colleagues, and media from around the world have all been asking the same questions: What’s eating Putin? What has driven him to start the largest war in Europe since World War II? What is driving him to threaten World War III, including the use of nuclear weapons?

My answer has been: It’s complicated. No single answer fully accounts for the display we are seeing of Vladimir Putin’s anger and grievance. Many Russian experts who know Putin well have been commenting on his mindset, but I want to lay out how I think about the picture. As I see it, at least eight different factors account for Putin’s erratic and dangerous behavior:

Read the rest at the Bulletin of Atomic Scientists