This chapter considers the function of consent in respect of the international laws on force and intervention, specifically in relation to so-called solicited actions undertaken by so-called third states. How ‘consent’ is implicated in the normative design of both force and intervention is explored by means of an historical assessment that takes on the cognate ideas of coercion and dictatorial interference. The chapter then moves to unpack the ambitions of and limitations for consent set forth more broadly within public international law, principally by analysing three resolutions of the Institut de droit international (IDI): on insurrection, on civil war, and on military assistance. The chapter also undertakes a detailed examination of the significance and mechanics of the operation of consent in other laws of the ius ad bellum (collective self-defence, counter-intervention, pro-democratic intervention, UN Security Council authorisation), quite apart from its role in governing the lawfulness of the practice of solicited action itself.

The past decade has seen outside states, coalitions or regional organisations lead military operations at the (real or alleged) ‘invitation’ of one of the parties embroiled in military strife – notably, in Mali, Syria, Yemen, and The Gambia. This chapter addresses key legal questions, starting with the validity of a government’s ‘consent’. Others include the legal nature and the effects of such consent, and how a government might lose its capacity to consent to military action in its own territory. The chapter includes analysis of the legal doctrines that might limit the lawfulness of the intervention despite such consent, including the invalidity of consent, the ‘negative equality’ doctrine or complete abstention, unlawful purposes, and other grounds of illegality, such as the inviting state’s complicity in international crimes. In the cases examined in the volume, the intervening states typically invoked multiple legal grounds, of which invitation is only one, and the UN Security Council has been intensely involved: the chapter appraises the legal significance of these novel features. It concludes with a summary of the trialogue method and an overview of the subsequent chapters.

This concluding chapter draws the central threads of the book together. It proceeds in five steps, providing conclusions, first, on the limitation of military intervention by invitation and, second, on the institutionalisation triggered by the increased importance of the UN Security Council in the operation of the law. It then takes up the question of whether Council practice may contribute to the development of the law, and it addresses the politicisation of the practice of consensual military intervention. Finally, it argues that while practice has been multilateralised as a result of the increased role the Security Council plays, we are in fact witness only to a ‘half-hearted multilateralisation’.