We all have a vague sense that social media is bad for our minds, for our children, and for our democracies. But the truth is that its reach and impact run far deeper than we have understood. Building on years of international reporting, Max Fisher tells the gripping and galling inside story of how Facebook, Twitter, YouTube, and other social network preyed on psychological frailties to create the algorithms that drive everyday users to extreme opinions and, increasingly, extreme actions. Traversing the planet, Fisher tracks the ubiquity of hate speech and its spillover into violence, ills that first festered in far-off locales, to their dark culmination in America during the pandemic, the 2020 election, and the Capitol Insurrection. The result, as Fisher shows, is a cultural shift toward a world in which people are polarized not by beliefs based on facts, but by misinformation, outrage, and fear.