From 1919 some voices were raised in Brittany to claim the right of the Breton people to dispose of themselves. Grouped around the newspaper Breiz Atao, a team of young activists pretends to lead Brittany to autonomy within the framework of a federal Europe, even to independence, which requires a redrawing of borders. Very quickly it was the Europe of the Treaties which was criticized, in a logic of rapprochement with other regional nationalisms, and with Germany, some nationals of which stirred up local claims. This Breton and European activism finds its most complete expression in two reviews: the Bulletin des minorités nationales en France, created in 1936, and quickly renamed Peuples et Frontières (Peoples and Borders). Why and how did a few Breton activists without an audience pretend to get involved in European geopolitics? What interest did their journal defend? After being disappointed by Panceltism, these Breton nationalists first turned to the oppressed minorities of France, who gathered in 1927 in a committee without a future. The federalism promoted by this committee finds new life in the Bulletin des minorités nationales en France, which soon spread to Europe under the name Peuples et Frontières, in accordance with the wishes of some German activists, including Gerhard von Tevenar. Consequently, the review defends German interests in Central Europe, since asking for the revision of the Treaties would make it possible to defend Breton interests in France. Largely, this monthly was moderated by Yann Fouéré, whose network extended to central Europe, that was considered as a laboratory.