The idea and practice of humanitarian intervention is a key feature in world politics. We are surrounded by debates about the deployment of military force to protect vulnerable populations and prevent atrocities. But the practice of humanitarian intervention has a lengthy and underexplored history which sheds a light on its limitations. This “element” offers the first concise and succinct history of humanitarian intervention as a tool of warfare and peacemaking in international politics. It traces the modern origins of the practice in transatlantic anti-slavery activism and attempts to regulate piracy. By discussing the nineteenth century evolution of the practice in various peripheral colonial or semi-colonial contexts (Ottoman empire, Africa) the book shows how humanitarian intervention operated within a highly selective framework of definition of what subjects are worthy of protection. The nineteenth-century boundaries of humanitarian intervention were coded in the constitution of the new institutions of world governance associated with the League of Nations and the United Nations. The element analyses how the postwar language of human rights,, the dynamics of decolonization and the cold war rivalries impacted the use of humanitarian intervention as a tool of peacemaking. The exploration of the historical context of humanitarian intervention also offers a clearer grasp of the changes in the technology of interventions – from naval blockades and international gendarmes to blue helmet peacemakers, precision airstrikes and drone warfare. This shift becomes clearer in the 1990s. The element explores the resurgence of humanitarian intervention in response to mass violence and genocides in Africa (Rwanda) and the Balkans (ex-Yugoslavia) which frame the gestation of the ‘right to protect’ doctrine. Finally, the element analyses the changes in the debate on humanitarian intervention brought by the war against terror in the dawn of the twenty-first century and, more recently, the outbreak of civil wars and international conflicts in Syria, Ukraine, and Gaza. Is the practice of humanitarian intervention a legitimate, even desirable, instrument of peacemaking? This element will approach this question by discussing what humanitarian intervention has been in the past two centuries and analysing its shortcomings.