The question of whether states or international bodies are morally and legally permitted — or obligated — to use military force against a sovereign state to protect that state's population from mass atrocities, genocide, or crimes against humanity — a question that pits two foundational principles of international order against each other: the sovereignty of states and the protection of human beings from their own governments.
The United Nations was built on a paradox. Its founding document proclaims universal human rights. Its founding principle is the sovereignty of member states. For most of its history, sovereignty won: what happened inside a state's borders was its own business. Rwanda changed that. Eight hundred thousand people were killed while a UN force watched and the Security Council debated. The lesson everyone drew was the same: something had to change. But there were two opposite lessons available — the world should intervene to stop atrocities, or the world should be more honest about when it will not. Neither has been fully adopted, and the tension between them runs through every humanitarian crisis since.