In the early weeks of the First World War, France experienced a patriotic revival, embodied in the term 'Union Sacree', in which an upsurge in religious faith became allied with the national cause. For many French Catholics, the conflict was perceived as a 'holy' war and it was believed that soldiers who were prepared to sacrifice their lives for the nation would go straight to heaven. By 1918, after four years of trench warfare and immense numbers...