American slaveholders before the Civil War oversaw an incredibly brutal economic system that generated enormous wealth for a tiny elite while denying enslaved Africans the most basic rights. But they also presided over American foreign policy, overseeing US territorial and economic expansion. As historian Matt Karp explains in This Vast Southern Empire: Slaveholders at the Helm of American Foreign Policy, they didn’t just want an independent slaveholding South — they wanted to spread their empire of slavery to the entire United States and beyond.

In November 2016, Karp spoke at the New School in New York City with historian Eric Foner, Dewitt Clinton professor of history at Columbia University and author of many books on the Civil War including Reconstruction: America’s Unfinished Revolution and The Fiery Trial: Abraham Lincoln and American Slavery. Karp is an assistant professor of history at Princeton University and a contributing editor at Jacobin.

This transcript of their talk has been edited. You can also listen to the discussion as a podcast here.