Empires are one of the most common forms of political structure in history—yet no empire is alike. We have our “standard” view of empire: perhaps the Romans, or the China of the Qin and Han Dynasties—vast polities that cover numerous different people, knit together by strong institutions from a political center.But where do, say, the empires of the steppe, like the Xiongnu or the Mongols, fit into our understanding of empire? Or the Portuguese empire, which got its start as an array of ports and forts in South and Southeast Asia? Or the Manchus, who waltzed into a collapsing Ming China and rapidly re-established its governing structures–with themselves at the head?These are just a handful of what Thomas Barfield calls exogenous, or “shadow” empires, which grow on the frontiers of larger, wealth-growing polities, in his most recent book Shadow Empires: An Alternative Imperial History (Princeton University Press, 2023).Shadow empires cannot exist without their hosts, extracting wealth from them—and yet, the most successful of them grow to become wealth creators in their own right, becoming what Barfield terms “endogenous empires.”In this interview, Thomas and I talk about empires—both the commonly-accepted kind and their shadow variants—and how we can differentiate between the many different kinds of empire throughout history.Thomas Barfield is professor of anthropology at Boston University. His books include Afghanistan: A Cultural and Political History (Princeton University Press: 2010) and The Perilous Frontier: Nomadic Empires and China, 221 BC to AD 1757 (Wiley-Blackwell: 1992).You can find more reviews, excerpts, interviews, and essays at The Asian Review of Books, including its review of Shadow Empires. Follow on Twitter at @BookReviewsAsia.Nicholas Gordon is an editor for a global magazine, and a reviewer for the Asian Review of Books. He can be found on Twitter at @nickrigordon.