This chapter argue that the political authority deployed through the early experiments of governance by the League of Nations was actually more limited than generally accounted for. If some of these missions, such as in Danzig and the Saar Basin, were given manyof the ‘trappings of sovereignty’, the actual practices of sovereignty were more limited than generally accounted for. Basing my analysis on archival research done at the Archives of the League of Nations in Geneva – analysing the “hidden transcripts” of League officials – I argue that League of Nations officials were far from being international governors, and authority in most cases resided firmly in specific European capitals.

Chapter 5 addresses the German–Polish Convention of 15 May 1922, a legal instrument that was negotiated with the direct participation of the League Secretariat and whose aim was the smooth partition of the multi-ethnic industrial region of Upper Silesia. It shows that while this treaty provided opportunities for ‘peace through law’, it ultimately failed to meet this expectation. After providing an overview of the Convention’s drafting process and its key features, notably its reliance on international procedural avenues to guarantee individual rights, the chapter examines these guarantees and how they came into being. It then focusses on the role of the president of the Mixed Commission for Upper Silesia, Felix Calonder, a vocal proponent of ‘peace through law’. In his role as local guarantor of minority rights, Calonder developed a systematic case law that was unequalled before the advent of the international human rights law bodies after the Second World War and foreshadowed some of the principles adopted by them. It concludes by reflecting on the various limitations that this law shared with other attempts to use legal techniques to solve interstate conflicts of the interwar period.

This form of international cooperation offered completely new possibilities for the suppression of a system of human trafficking that operated across oceans and continents, but at the same time it conflicted with the interests of particular states and their own mutual rivalries and on several occasions threatened to founder on the limitations imposed by national sovereign rights. Alongside the viability of the agreed measure, then, Chapter 6 looks at the diplomatic wrangling by which the British government tried to secure treaty obligations from as many states as possible and to overcome massive political resistance, notably from Spain, Portugal, Brazil, France and the United States. Yet this decades-long process of negotiation produced a mounting international consensus, particularly from the mid-1840s onwards, condemning slavery as a ‘crime against humanity’. One telling sign of this new moral climate was the emergence of one of the first international treaty regimes, which extended from Europe across North and South America and the Arab World to East and West Africa. Its foundational idea was to enforce an agreed humanitarian norms by military means if necessary. The fight against the slave trade, it is argued, gave rise to a new conception of intervention, and abolitionism became established as a key international guiding norm for ‘civilisational’ action in the long nineteenth century.