Lavenia's work seems to be a natural continuation of the Soldati del papa (Pope's soldiers), edited by Carocci in 2003 and written by Giampiero Brunelli. If Brunelli's book is an analysis of the military policy and nobility in the ecclesiastical state from the second half of sixteenth century to the first half of the seventeenth, done from a military and political point of view, Lavenia's investigates another kind of church army and policy (both Catholic and Protestant): churchmen (and accompanying treatises) serving as chaplains among soldiers, and the position of the church about war and armies. It is an investigation into war and the catechesis developing until the First World War to inform first the condottieri and chaplains about the idea of the right (just) war, and then soldiers themselves (eighteenth and nineteenth centuries) about the right way to fight. In this way this book can be inserted in that branch of studies concerning the relation between armies’ discipline and religion (which Lavenia reviews at length) and concerning the composition of the armies.

The volume is a scrupulous analysis of the evolution of clerical and lay treatises, considering the meaning of right war (ius ad bellum) and the right way of fighting (ius in bellum). An accurate reflection of the Catholic treatises concerning war is the core of the volume, comprising the first four chapters, from Saint Augustine (fourth–fifth century), to Possevino and Sailly (end of sixteenth century), through Giovio, and, above all, the dualism between Erasmus and Machiavelli that will influence all following thoughts about war, both Catholic and Protestant. The author does not forget, even if the dedicated space is not large, the American reality, with Cotton Mather and his sermons. The modification of the treatises before and after the Peace of Westphalia (1648) is the subject of the sixth chapter. Lavenia clearly explains how catechetical treatises had been modified by the events of the Thirty Years’ War, finding a new public in soldiers, not only in kings or men at arms. Lavenia highlights the chronological evolution of such treatises, their transformations from a reflection on ius ad bellum to ius in bellum—from what was considered the right war to what should be considered the right way of fighting. This new reflection becomes the preamble to new books for soldiers (educational treatises) that come together with military reforms of the eighteenth century.

A significant characteristic of the book is the successful link between the analyzed treatises and contemporary that influenced their writing. With simple but not banal writing, the book meets the interest of historians as well as common people who want to know the past. The author tries to encourage people to go deeper, providing readers with some easy-to-find bibliographical references. This attempt by Lavenia is commendable in a historical period when, more and more often, history is transformed into fiction or into anecdotes without traces of depth.