The Peace of Westphalia in 1648 has given rise to interpretations that evolved over time. Il is still used to structure reflections over international relations’ overall evolution. Here, a modern times historian gives his own vision of his historic landmark. The Münster and Osnabrück Treaties would play the part of terminus as quem : they settled Europe’s religious layout by reducing the role of spiritual choices in conflicts, and they settled the political order by neatly delimiting the various States’ identity and position. These agreements also represented a terminus a quo since they set rules for international dialogue through the art of diplomacy and reinforced the notion of balance in the face of any temptation of universal monarchy. The led princes to gradually move behind the people they were governing, thus promoting nations’ self-assertion. By limiting great geopolitical upheavals, they helped liberating forces for the European expansion in the world.