In late October 1956, the Soviet army crushed a burgeoning rebellion in Hungary, ostensibly upon the invitation of the Hungarian government, and allegedly in conformity with the provisions of the Warsaw Pact. While the intervention was widely condemned, international law could not prevent the Soviet invasion nor secure the USSR's withdrawal from Hungary. Seven decades later, this Chapter analyses the Soviet intervention under jus ad bellum. It focuses on the positions of relevant actors in real-time, as well as on the enduring aspects of the affair. As the Chapter reveals, the Hungary intervention presented dilemmas that plague the law on the use of force even in contemporary times. It raised questions that remain burning today, such as the role of consent in legalizing external forcible intervention, the ability of international law to face superpowers, and the dialectics between effectiveness and legitimacy in the determination of lawful authority during internal strife.