The paper tries to go back over some of the issues that seem to be common to all of the European Christian churches (but North American too) during the First World War, and presents some examples of data extrapolated from the Austro-Hungarian situation. It will be examined the attitude of the American catholic newspaper “The Boston Pilot” too. These are issues that would be destined to be rooted in the life of the churches for many years to come. Going beyond the war years an effort should be made to reconstruct how, during the First World War, a process was started which led to the construction of the theological-political-historical framework that allowed for the construction of a religion of the homeland as a path for that nationalisation of the masses that then took on a totalitarian face. It is undeniable that the First World War provided a fundamental contribution, through the projection of the theme of nation by way of religious values and the consolidation of a self-understanding of the war as a religious war, outlining in more robust terms the sacralisation of politics that would represent one of the dominant notes of the Right-wing regimes and movements in the 20th century, whose development cannot be separated from the War experience itself. In this sense, it seems as though the Great War has been endowed with a precise as well as decisive genetic function vis-à-vis the manifestation of the immediately ensuing totalitarianism regimes. Hence, if we assume a scenario of the sacralisation of politics and the Fatherland, we can conclude that even if the concept of war of religion can only be partially assumed and limited to just some areas, the concept of religious war instead appears to be fully applicable to what has hitherto been examined.