Historian Daniel Macfarlane introduces his new book, Natural Allies: Environment, Energy, and the History of US-Canada Relations from McGill-Queen's University Press. The book shows that the Canada-U.S. energy/environmental relationship is historically the most consequential in the world, spawning important changes in international environmental law and transboundary governance, while also fostering the voracious consumption of resources and and large-scale ecosystem change. In addition to analyzing this history, Macfarlane offers the concept of "natural security" as a potential guide to international environmental agreements and pathways.