Mounting evidence suggests that non-consensual military intervention is most often a poor instrument for alleviating mass suffering. Thus, a growing number of scholars and practitioners argue that the international toolbox for protecting populations should also contain non-coercive tools for assisting states and enhancing their capacities. But while studies of the history of military intervention proliferate, past thinking about duties of assistance and capacity-building remains relatively neglected. This article seeks to rectify this state of affairs by analyzing and seeking insights from the detailed treatment of non-coercive means of discharging duties to others offered by the eighteenth-century Swiss jurist and diplomat Emer de Vattel. Drawing on Leibniz's conception of "perfection," Vattel argued that states have duties to contribute to the perfection of those beyond their borders insofar as they can without doing an "essential injury" to themselves. While some of his claims about duties may be uncontroversial today, others remain subject to ongoing contestation, and still others have been forgotten and demand renewed attention. Crucially, while Vattel acknowledged the need for prudence, he also demanded that states be willing to make sacrifices for the sake of vulnerable strangers. He framed the cultivation of ever greater ability to assist others as a fundamental aspect of a state's own self-perfection.