Most of us don’t think of United States history as an imperial history, but the facts are there. The law and policy surrounding westward expansion, off-continent acquisitions, and a worldwide network of hundreds of bases reveal much about how and why the United States grew as it did.

Last month, David Priess spoke with Daniel Immerwahr, associate professor of history at Northwestern University and author of “How to Hide an Empire.” They talked about everything from what the Constitution says about lands west of the thirteen colonies, to the critical role of the Guano Islands in U.S. history, to the famous Insular Cases, to how military access agreements and long-term leases help the United States avoid a truly territorial empire.