The chapters of this book were written to be delivered as the 2019 Conway Lectures at the University of Notre Dame and the 2020 Carlyle Lectures at Oxford University. I would first therefore like to thank both institutions for the honor of being invited to give these lectures, and in particular Thomas Burman at Notre Dame and George Garnett at Oxford for issuing the invitations and offering splendid hospitality. I would also like to thank Megan Hall and Graham Lockey for their work in organizing these events and Stephen Little at the University of Notre Dame Press for his enthusiasm for the book project.