At first, Xenopol served as a prosecutor in Iași, but he later decided to dedicate himself to the study of history.

[4] In his 1899 French-language Les Principes fondamentaux de l'histoire ("The Fundamental Principles of History"), his work most well known internationally,[citation needed] he argued for history being a true science which follows clearly defined laws and logic, through which the reasons for historical processes could be clearly defined.

Concerning events nearly two millennia in the past and being supported by multiple archaeological findings, it was still contested by some historians.

[citation needed] It had, however, very concrete political implications – the Roman origin implying that Romanians are inherently different from their Slavic and Magyar neighbors.

This, despite his disagreement with radical nationalists and objection to violence against Jews,[5] unfortunately also translated to Xenopol being a noted antisemite and collaborator of A. C. Cuza.