On April 6, 1994, a plane was hit by a missile over the Rwandan capital of Kigali. Everyone onboard was killed, including Rwanda’s president, Juvénal Habyarimana.

Even twenty years later, it remains uncertain who shot down the plane. But what happened immediately afterwards is very much known, seared into the minds of those who bore witness and branded forever on Rwanda’s soul. Hutu extremists blamed the Tutsi ethnic minority for the president’s killing and began a program of mass extermination. By the time they were finished, 800,000 Tutsis and moderate Hutus were dead, most of them hacked apart with medieval weapons like machetes and axes.

The genocide was marked by the speed of its executioners—400 people killed an hour, five times the rate of the Holocaust—and the torpor of the rest of the world. The United Nations Peacekeeping division, under the leadership of future UN secretary general Kofi Annan, rebuffed any attempts at military intervention. The head of the UN mission in Rwanda, General Roméo Dallaire, was prohibited from using meaningful force. When Rwanda’s moderate prime minister was attacked and killed, the peacekeepers guarding her couldn’t fight back. The Clinton administration, spooked after its hasty withdrawal from Somalia, wanted nothing to do with Rwanda. As the bodies piled up, the State Department waltzed around the word “genocide.”

Today Rwanda still haunts international thinking. If we imagine a linear scale with the extreme poles of isolationism—close our doors to the rest of the world—or neoconservatism—toss bombs everywhere our values are threatened—most people, including this writer, fall somewhere in the middle, believing we should intervene when some conception of America’s national interests are in danger. In Rwanda, we had no interests of any sort—no trading relationship, no military bases, no bonhomie with its leaders. The Clinton administration knew this, didn’t act, and nearly a million people were slaughtered.

Hawks like to blame international crises on American “weakness” or “retreat from the world.” These claims are often bogus, but in the case of Rwanda they were absolutely correct. The killers had a chilling awareness of how the retreat from Somalia was darkening American foreign policy. Three months before the genocide began, Dallaire was contacted by an informant named Jean-Pierre who was affiliated with the Interahamwe, a radical Hutu militia that would carry out much of the killing. Jean-Pierre said his group was planning to murder some of Dallaire’s Belgian peacekeepers because they believed, post-Mogadishu, it would scare the UN away. Sure enough, ten Belgians were kidnapped and killed, and Belgium withdrew its peacekeeping commitment, the centerpiece of Dallaire’s small force.

When it became clear Rwanda was about to unspool, French soldiers arrived to evacuate Western personnel, and Western personnel only. Linda Melvern describes the scene at a school as it dawned on the 2,000 Tutsi refugees trapped inside that the seemingly godsend French weren’t there to help them:

People tried to hang on to lorries. The Belgian soldiers brandished their weapons, and fired into the air. The French soldiers prevented others from getting too near to the peacekeepers. The French promised the people that they would stay. At 13.45 the last Belgian soldier pulled out of the school. Then the French soldiers left. People started to cry. The bourgmestre, a member of Rwanda’s Parti Social Démocrate (PSD), the centre-left opposition party, tried to calm everyone, and told them that they must defend themselves. `But we had no weapons, not even a stick,’ someone said.

The Tutsis were later herded out of the school by Hutu militants and slaughtered.

This is enraging not only because the refugees might have been saved, but because for a fleeting moment the intervention force was there—the peacekeepers and the French soldiers. It might not have been enough, but it certainly would have stymied the bloodshed. Instead, the United Nations later voted to carve out the peacekeepers by a further 90 percent, leaving Dallaire with only 270 meagerly equipped troops.

Dallaire would later write in his memoir:

Could we have prevented the resumption of the civil war and the genocide? The short answer is yes. If UNAMIR [The UN Assistance Mission for Rwanda] had received the modest increase of troops and capabilities we requested in the first week, could we have stopped the killings? Yes, absolutely.

The United States doesn’t have a moral imperative to intercede everywhere there’s trouble in the world, and often when it does, the host country is left worse for wear. But what about when seven people are being murdered a minute? And a small investment of troops would have saved an enormous number of lives? Doesn’t the moral calculus demand that, to recycle a banality used far too often in foreign policy, something must be done? This wasn’t some quixotic project to defuse decades-old tensions between the Hutus and Tutsis, or rebuild Rwanda from the ground up; it was about protecting lives.

Instead 70 percent of the Tutsis and 20 percent of Rwanda’s population were killed. The innocent were corralled into churches and schools where they were slaughtered. Sexual assault was used as a weapon, affecting between 100,000 and 250,000 women. Extremists released HIV-positive patients from hospitals and formed them into rape squads to target Tutsis. “It was as if we were taken over by Satan,” one Hutu farmer later told PBS. A mass exodus of both Tutsis and Hutus to neighboring Zaire sparked two bloody civil wars that killed millions.

Dallaire, who did everything short of lighting himself on fire in Kigali to get the UN’s attention, was denied over and over again. His memoir, Shake Hands With the Devil, written with military precision, is a wrenching account of the mission that left him depressed and suicidal. “I think some part of me wanted to join the legions of the dead, whom I felt I had failed,” he writes. “I could not face the thought of leaving Rwanda alive after so many people had died.”

Of the West, which left Rwanda very much alive, questions must be asked on this twentieth anniversary of the slaughter. At what point must troops be deployed to save lives? And what happens the next time a nation on the other side of the world is thrown under the dark curtain of genocide?