The United Nations (UN) Trusteeship period during 1948 and 1960 is relevant for Cameroon’s history till today: On the one hand, the Trusteeship Council played a significant role in the resolution of a highly violent decolonization conflict; on the other hand, the significance and the legacies of the trusteeship system are demonstrated by the lasting reference of the territorial logics and structures it established in the current Anglophone crisis. By drawing on the case of Cameroon’s UN-led Trusteeship decolonization, the chapter, thus, focuses on the construction of power, legitimacy, and security by using securitization approaches in a postcolonial lens. Empirically the paper provides insights into the transition toward independence within the situation of trusteeship and the ways anti-colonial activists and the French mandate authority confronted each other with their narrations of threats, insecurity, and divergent views on the future statehood. As such, the chapter contributes to discussions on trusteeships that experienced war, focusing on the role of global institutions in international relations. Based on archival material, the paper scrutinizes narratives and imaginations that French, Cameroonian elites, and UN actors developed, in order to secure legitimacy and gain political power on the global, transnational, and national level against the background of the escalating violent conflict.