Between April and July of 1994 — one hundred days — between 500,000 and one million Tutsi and moderate Hutu Rwandans were killed by their neighbours, mostly with machetes, in a genocide that had been openly planned for years. The trigger was the shooting-down of the president's plane on April 6; the killing began within hours, too fast and too organized to be spontaneous. The radio station RTLM broadcast lists of names and addresses and called the victims inyenzi — cockroaches. The killings were organized, denounced in advance by human rights groups, and televised in real time. The United Nations had peacekeepers on the ground under General Roméo Dallaire. They were ordered not to intervene. The United States, still emotionally raw from Mogadishu the previous October, refused to even call the killings genocide because doing so would have triggered legal obligations to act.
Rwanda is the case study of how the international system handles a genocide it sees coming, watches happen, and chooses not to stop. The Belgian colonial administration had sharpened a fluid Hutu-Tutsi distinction into a quasi-racial caste system, issuing identity cards that fixed each Rwandan's group; independence-era Hutu nationalists had inverted and weaponized it to organize political power. The 1994 killings were not a sudden eruption but the implementation of a plan — militias called the Interahamwe had been armed and rehearsed in advance. As the slaughter began, the UN withdrew most of its force rather than reinforce it. The world's reaction afterwards — UN reform, the 'Responsibility to Protect' doctrine, the ad hoc International Criminal Tribunal for Rwanda — was the moral and institutional response to having watched. More lastingly, the permanent International Criminal Court, whose 1998 Rome Statute was driven in part by the post-Rwandan conviction that some kind of standing legal architecture had to exist for these crimes. Rwanda itself, under Paul Kagame's authoritarian post-genocide government, achieved one of Africa's fastest economic recoveries and pioneered the community gacaca courts to try the accused — at the price of a political openness it has not been willing to allow.
Every subsequent atrocity — Darfur, Syria, Myanmar, Tigray, Gaza — has been measured against Rwanda as the floor of what the international community failed to prevent. Bill Clinton later called his inaction the worst regret of his presidency. The phrase 'never again' was first used after the Holocaust; after Rwanda, it has been invoked after every subsequent failure, until it reads less as a vow than as an epitaph. The pattern — early warning ignored, legal triggers dodged, intervention arriving too late or not at all — has not been encouraging.