Thomas J. Barfield is professor of anthropology at Boston University. His new book, Shadow Empires, explores how distinctly different types of empires arose and sustained themselves as the dominant polities of Eurasia and North Africa for 2,500 years before disappearing in the 20th century. He is a renowned historian of Central Eurasia and the author of The Central Asian Arabs of Afghanistan, The Perilous Frontier: Nomadic Empires and China, 221 BC to AD 1757, Afghanistan: An Atlas of Indigenous Domestic Architecture, and Afghanistan: A Cultural and Political History (revised and expanded second edition 2022, Princeton University Press).