The protection of nationals abroad: from ‘unlawful yet tolerated’ to ‘unlawful and intolerable’.

The unilateral use of force by a state to protect its nationals abroad (PNA) is one of the most contested issues in contemporary international law, creating a dangerous ambiguity in the legal framework governing the use of force. This chapter provides a detailed analysis of the PNA doctrine's legal basis, operational logic, and normative risks. It argues that the doctrine's humanitarian appeal often masks its function as a vessel for strategic interests, allowing states to circumvent the UN Charter’s prohibition on the use of force.

The chapter first deconstructs the main doctrinal justifications for PNA, concluding that it does not constitute a free-standing rule of customary international law and rarely satisfies the strict conditions for self-defence under Article 51 of the UN Charter. It then assesses the doctrine's operational history, highlighting its susceptibility to abuse as a pretext for unlawful aggression, as seen in cases from the Suez Crisis to Russia's invasions of Ukraine. To capture the nuanced international response to these acts, the chapter proposes a novel typology that maps PNA interventions along a continuum of political reception, from unlawful yet tolerated evacuations to unlawful and intolerable coercive interventions. The chapter concludes that while the pragmatic political acceptance of certain limited rescue missions exists, this toleration does not amount to legality, and the absence of condemnation cannot be interpreted as the formation of a new legal norm. The PNA doctrine thus remains a source of legal fragility, capable of eroding the foundations of the jus ad bellum.