Amitav Ghosh is the author of the Ibis trilogy, comprising Sea of Poppies (shortlisted for the 2008 Man Booker Prize), River of Smoke, and Flood of Fire. His other books include The Circle of Reason, In an Antique Land, The Glass Palace, and The Great Derangement. This essay is adapted from his new book, Smoke and Ashes: Opium’s Hidden Histories, published by Farrar, Straus and Giroux.