The atrocity, which killed more than 800,000 people in 100 days, began 20 years ago this Monday. Things have changed a lot since then, and Rwanda is widely considered a post-conflict success story. But the years have done little to erase the memories of many survivors who are still torn between punishing and forgiving the perpetrators. The genocide is also a painful reminder of the consequences of the international community’s indifference in the face of mass murder. The lesson still resonates when discussing possible intervention in conflicts today, from the Central African Republic to Syria.