On the basis of a critical challenge to the traditional theoretical edifice, Kelsen, Kunz, and Verdross developed their own construct of international law at the beginning of the 1920s. In contrast to Triepel and other dualists, their own “objective” theory proceeded from a unitary view of the law. From the monistic perspective, international law and national law were parts of a single, unitary legal system. Moreover, this foundation was to be used to demonstrate that international law – despite the complaints of deniers and doubters – could be conceived as a law fortified with the power of coercion. To that extent it could be subsumed under a uniform legal concept along with domestic law. International law and national law were thus part of a unitary system of norms endowed with the power of coercion. Within this overarching system, the thesis of the primacy of the law of nations was then used to place international law above national law. This objective edifice of international law reflected the confidence of Kelsen and his students in the effectiveness of the medium of international law. In the wake of the First World War, the “new” international law in the era of the League of Nations was to be available to international politics as an effective instrument for securing the peace.

Constructing a unitary system

The roots of the systems idea, which exerted a substantial influence on Kelsen's articulation of international law, are more difficult to pin down than the clearly neo-Kantian works following his Main Problems of State Law would suggest.