Written by an award-winning historian of science and technology, this book describes the top four mega-dangers facing humankind - climate change, nukes, pandemics, and AI. It outlines the solutions that have been tried, and analyses why they have thus far fallen short. These four exponential dangers present a special kind of challenge that urgently requires planet-level responses, yet today's international institutions have so far failed to meet this need. The book lays out a realistic pathway for gradually modifying the United Nations over the coming century so that it can become more effective at coordinating global solutions to humanity's problems. Neither optimistic nor pessimistic - but pragmatic and constructive - the book explores how to move past ideological polarization and global political fragmentation. Unafraid to take intellectual risks, Safe Passage sketches a plausible roadmap toward a safer, more democratic future for us all.