Forcible PNA is a concept that existed long before the UN Charter and thus the current international legal regime on the use of force. Historical review and development of the doctrine’s occurrence demonstrates its role in the formation of modern states, and its timeless significance for superpowers, as a tool to preserve their international dominance. In addition, historical insights connect the dots between the doctrine and its relationship with the institutions of nationality and sovereignty. The doctrine’s development is a manifestation of how the sovereign state concept progressed through time. Therefore, this chapter delves into early affirmations of the doctrine, and it examines whether a customary rule permitting recourse to force in the name of nationals’ protection abroad existed before the establishment of the UN Charter.