The French army has long maintained a special relationship with the Catholic Church and the Republic. In the 1880s, Republicans engage in a policy of secularization of public institutions, including the military, which will be characterized by moderate reforms opportunists (1879 to 1898), followed by the deep distrust of radicals against military (1899 to 1914), especially after the Dreyfus affair seen as the developer of a mythical "alliance of the sword and brush." In this work, Xavier Boniface focuses on the triangular relationship of the army, the Church and the Republic struggling with the changes, tensions and political crises of this pivotal period preceding the Great War. Through large files - the adaptation of military chaplaincy in the case of records, through military service imposed seminarians or enforcement by the army during the application of secular laws - the author depicts the difficulties of military to accept the new regime and its system of values to the Sacred Union in 1914.