This chapter clarifies some key terms and situates the phenomenon of sharing international obligations within the current body of international legal doctrine. The conceptualization of shared obligations takes place in the context of the international law of obligations, and it is first discussed what is meant when reference is made to this body of law. The focus then turns to the concept of shared responsibility in international law, and some preliminary reflections are offered on how the concept of shared obligations contributes to the ongoing discussion on problems of shared responsibility in legal doctrine. It is then discussed how the idea of sharing international obligations has been recognized in international legal literature and proceedings before international courts, reflecting an (at times implicit) assumption that the sharing of international obligations has relevant legal implications. Nevertheless, the notion of shared obligations remains conceptually underdeveloped. Finally, it is set out how this lack of conceptualization of shared obligations is not a result of the notion’s irrelevance but may be explained – at least in part – by a few fundamental choices that have been made during the ILC’s project of codification and progressive development of the international law of obligations.

This chapter sets out to capture the practical phenomenon of sharing international obligations by developing a concept of shared obligations. In the stipulation of this concept, the chapter draws from and engages with various scenarios in practice that involve obligations incumbent on multiple states or international organizations, including those obligations that have been designated as ‘shared’, ‘joint’ or ‘collective’ in legal literature. By expanding on three elements that characterize a shared obligation, it is argued that the main characteristic that distinguishes obligations that are shared from obligations that are not shared is the existence of a connection between the bearers of an obligation in the performance of that obligation. It is this particular relationship between the bearers of a shared obligation that gives rise to questions regarding performance and international responsibility: who is bound to do what and, subsequently, who can be held responsible for what in case of a breach? All in all, qualifying a particular obligation as ‘shared’ brings such questions to the forefront, and thereby constitutes the first step towards addressing them.

The analysis in this chapter proceeds from the assumption that shared responsibility for a breach of a shared obligation has been established and focuses on the content of that responsibility. In the case that secondary obligations of reparation or cessation arise, what can be claimed from which responsible actor, and to what extent is this influenced by the fact that the underlying primary obligation is shared? And if injured parties wish to effectuate these secondary obligations through international adjudication, are there any obstacles to the claiming of cessation and reparation? It will ultimately be argued that conceiving of the content of shared responsibility as consisting of shared obligations incumbent on all responsible actors can help untangle which of the responsible states or international organizations is bound to do what in terms of cessation and reparation. In this context, the distinction between divisible and indivisible shared obligations has an important role to play. After all, determining whether responsible actors are each bound only to their own share of cessation or reparation or whether, alternatively, all of them become bound to achieve a common result has direct implications for what can be claimed from whom.

Contrary to the presumption that relational accounts of International Relations are inherently normative, this chapter offers a radical empiricist account of relationalism to explain the complex processes of nuclear sovereignty in the United States. The chapter argues that the bias for methodological individualism in International Relations and Security Studies obscures the processes and systems that make the communication and control of thousands of nuclear weapons possible. Rather than a sovereign presidential command enacting nuclear decisions, the chapter argues that the vast assemblage of informatic networks, satellites, coded exchanges, preplanned scenarios, and preexisting relations of enmity are the ecosystem which makes something that appears as sovereignty possible. To put it more simply, sovereignty is designed, built, and deployed, not delegated or ordained.

This chapter addresses the challenge of endogeneity, testing Master Hypothesis 4. Some critics of the grievance-based literature argue that endogeneity may undermine the link between exclusion and conflict, and by implication the opposite one linking inclusion to peace. Endogeneity derives from the fact that the governments' decisions to include or exclude could be motivated by the anticipation of conflict. We counter this threat to inference by articulating a causal pathway that explains ethnic groups' access to power independently of conflict. Focusing on postcolonial states, we exploit differences in colonial empires' strategies of rule to model which ethnic groups were represented in government at the time of independence. This identification strategy allows for estimating the exogenous effect of inclusiveness on conflict. We find strong and systematic evidence that - at least for the post-colonial world - inclusion in governmental power sharing systematically reduces the likelihood that ethnic groups become involved in ethnic civil war. Our instrumental-variable analysis confirms Master Hypothesis 4, because we have found that governments tend to co-opt potential rebels rather than excluding them.