This chapter deals with questions of sovereignty, territory and jurisdiction during the League of Nations era. It discusses how the concept of sovereignty developed until the League era and how it was understood then. Questions of territory and jurisdiction are closely linked with sovereignty, but, given the immense scope of this topic, it will only be considered as far as it affects the central substance of the chapter. This general exposition of the concept of sovereignty will be followed by an explication how the interwar period saw the emergence of, first, its general principle of horizontal protection of the territorial and jurisdictional aspect of states by international law; second, structured exceptions to this principle qua its vertical limitation of sovereignty through the League system; and third, curious cases where the territorial and jurisdictional powers of states had to be reconciled with other innovative legal principles such as human rights and self-determination. These explications will be illustrated and substantiated by a selection of the relevant cases decided by the Permanent Court of International Justice and other judicial bodies.

The League of Nations was the first permanent international organisation with a general mandate. Its establishment is widely regarded as having had a significant, if elusive, impact upon international law, which became centred on international institutions. These three aspects of the League – its permanence, the generality of its mandate, and the ’institutional turn’ it brought to international law – lie at the heart of the assumed significance of the League for contemporary international lawyers. They are regarded as the League’s principal innovations and central components of its legacy, often without much interrogation and rarely subject to sustained analysis. This chapter offers analysis and interrogation to nuance claims about the League’s innovations. It presents the League as an institution whose grand designs often failed, but which innovated quietly and gradually. Above all, it shifts the focus away from the perceived ’breakthrough’ of 1919, and highlights the evolutionary nature of the League, which adapted throughout its life.

The distinction between international and domestic law plays an essential function in the establishment of international law as an autonomous order. During the lifespan of the League, this distinction was contested by scholars and judges in increasingly sophisticated ways. This process culminated in the debate between monists and dualists. However, the formal conceptual foundations of this debate meant that it failed to take account of the way that bureaucrats, officials and experts at the League adopted equally sophisticated normative strategies as part of the ‘experiment of international administration’. Such strategies, which lay at the heart of attempts to promote the ‘well-being and development’ of peoples subject to mandatory rule and foster co-operation across social and economic fields, creatively transformed conventional understandings of the relationship between international law and domestic law. This chapter juxtaposes these simultaneous, countervailing trends of formalisation and deformalisation in international law and administration to offer fresh insight into the crucial formative period in the history of the distinction between international law and municipal law.

The interwar years are the shortest period covered in these volumes, and perhaps the most intense and eventful one. So many things happened in the short course of this quarter of a century that it would deserve an entire Cambridge History series of its own. Unlike other volumes, whose temporal boundaries are harder to establish, this one does not pose a problem. It is firmly locked between the iron parentheses of two devastating catastrophes, if such a pleonasm may be allowed.