When the Franco-Prussian War broke out, Gabriel Monod, with his cousins Alfred and Sarah Monod, organized an ambulance with which he followed the whole campaign, from Sedan to Le Mans. He wrote a small book of memoirs of this campaign, Allemands et Français (1871), in which he spoke of the conquerors without bitterness; this attitude was all the more praiseworthy as his mother was originally from Alsace, and he was unable to resign himself to the loss of Alsace and Lorraine.
The war being over he returned to teaching. At this period of his life he wrote Grégoire de Tours et Marius d'Avenche (1872); Frédégaire, whose history, taken from original manuscripts, he published in 1885; a translation of a book of W. Junghans, Histoire critique des règnes de Childerich et de Chlodovech, with introduction and notes (1879); Études critiques sur les sources de l'histoire carolingienne (1898, 1st part only published); and Bibliographie de l'histoire de France (1888). He himself said that his pupils were his best books; he intended to teach them not so much new facts as the way to study, endeavouring to develop in them an idea of criticism and truth. They showed their gratitude by dedicating a book to him in 1896, Études d'histoire du moyen âge, and after his retirement in 1905 by having his features engraved on a slab (see À Gabriel Monod, en souvenir de son enseignement: École pratique des hautes études, 1868-1905, École normale supérieure, 1880-1904. May 26, 1907).
In 1875 he founded the Revue Historique, which rapidly became a great authority on scientific education. Some of his articles in this and other periodicals have been put together in book form, Les Maîtres de l'histoire: Ernest Renan, Hippolyte Taine, Jules Michelet (1894); Portraits et souvenirs (1897: on Victor Hugo, Fustel de Coulanges, Victor Duruy, etc.)