In international legal historiography, it becomes a commonplace that the successful resolution of the Alabama dispute between Britain and the US by the 1872 Geneva Tribunal of arbitration – the 1872 Alabama arbitration – kindled the progressivist enthusiasm of liberal internationalists for projects of humanitarianism, the codification of international law, and international arbitration. The article aims to take this scholarship further by arguing that, against this backdrop of reformist enthusiasm for international law, two transnational social reform movements – pacifist internationalism and legalist internationalism – converged in a joint effort of social and intellectual mobilization in furtherance of an ordered system of international law and its judicial application in practice. The epitome of this encounter was the almost simultaneous creation of the International Law Association and the Institut de Droit International in 1873. The article shows that international jurists sought to delineate the nascent modern international law profession by strategically distancing their scientific cause of international law from the one embarked on by their pacifist counterparts. By demarcating international legal science in contrast to the contemporary pacifist activism of international law, international jurists set the parameters of their social networks, and manoeuvred for professional outreach. Yet it is precisely by bringing back the pacifist antithesis that had been deliberately relegated into the secondary by international jurists – ‘the men of 1873’ – that some previously under-emphasized aspects of the sensibility of l’esprit d’internationalité can be grasped.