Ephraim Emerton, an American educator, translator, author and historian, presented in this book a critical study on the work of the Marsiglio of Padua, namely The Defensor pacis, which, written as early as 1324, garnered heated discussion around him for the next century. The tract Defensor pacis itself is said to have laid the foundations for the doctrines of popular sovereignty. As for the presented book, in addition to the analysis of the tract itself, Emerton also studied the biography of Marsiglio of Padua.