on an equal basis is very new in historical terms. It is a great experiment. The history of humankind is a story of us versus them. Hobbes had it wrong: the state isn't needed to keep individuals from slaughtering each other; it's needed to keep groups from slaughtering each other. And yet, Mounk argues, group identity is both deeply rooted and quite malleable. He tells the story of two tribes in Southeastern Africa who hate each other in one country, where they compete for political power, while just across the border in a neighboring country they partner closely against a much larger array of more alien rivals. There's actually a lot of this around the world: he offers a brilliant tour across time and space of how groups change footing from conflict to cooperation, making the point that no community is beyond all hope of conciliation and unity. But groups have to come together as equals, on a level playing field, or else true integration is impossible. This remains the challenging task it has always been, and Mounk brings enormous reserves of expertise, wisdom and empathy to the work of showing us the paths to get there. The forces on all sides making cross-cultural contact difficult are seemingly everywhere on the rise; more bridges are being blown up than are being built. It's tempting for some to argue that all we can do is retreat and argue our respective corners. That way lies disaster, he argues passionately. There is a legitimate form of patriotism we can all embrace. Indeed, we must, for the failure of this great experiment in democracy is simply not an option. The Great Experiment is that rare book that offers both a profound understanding of the problem behind all of our other problems of collective action, and genuine hope for our human capacity to solve it.