Zimmermann, Michel Keywords: Middle Ages | International law | Legal history | Mots clefs: Moyen Age | Droit international | Histoire du droit | ABSTRACT For the majority of internationalists of the second half of the XIXth century and at the beginning of the XXth century, there is no doubt that the law of nations did not exist in the Middle Ages and that it made its appearance only after the Peace of Westphalia in 1648, writes Michel Zimmermann. On the contrary, for the great French writers of the first half of the XIXth century, it was contestable that a very developed international l…