The United Nations has called it the greatest crisis in the world. The United States calls it genocide.

It's happening in the African nation of Sudan, and 60 Minutes went to see for ourselves. What we saw and what you will see again tonight is evidence of a government-backed campaign to wipe out a race.

There are at least 180,000 dead and more than 2 million on the run. It all started two years ago in a part of Sudan called Darfur, where rebels looking for a measure of freedom revolted against Sudan's authoritarian Islamic government.

The government apparently decided to end the revolt by trying to wipe out all of the native Africans in Darfur, to clear the territory for Arabs.

We should tell you that some of the evidence of the killing that we found is hard to watch. But, as we did last fall, we will start with the survivors. They are the innocent victims, pouring across the border of Sudan into Chad.

Correspondent Scott Pelley reports.

traveled to the middle of Africa. There are refugee camps up and down the Chad-Sudan border. Some are larger; others smaller.

One camp has about 19,000 refugees, but in the entire region, there are 189,000 refugees, and the United Nations is planning for another 100,000 on top of that. One camp is the farthest north, which means it's in the driest part of the Sahara. Walking around it, you are struck by one thing. If this is better than where they came from, imagine what they are fleeing.

Pelley visits one of the villages burning in Sudan. The Sudanese government has unleashed African Arabs, called the Janjaweed, to wipe out tribal blacks. The name "Sudan," ironically, is Arabic, meaning "land of the blacks." But the Janjaweed is rewriting that history in blood. Janjaweed, by the way, has a translation, too. It means "evil on horseback."

John Prendergast, who was director of African Affairs at the National Security Council for the Clinton White House, says that these tribal blacks have "been subjected to one of the most brutal campaigns of ethnic cleansing that Africa has ever seen."

Prendergast is now with the International Crisis Group, a human rights organization documenting the disaster in Sudan and neighboring Chad.

"A government-made hurricane hit Darfur ... using these Janjaweed militias," Prendergast says. "And the human debris has washed up on the shores of Chad."

The refugees are from Sudan's western province, Darfur, which is about the size of Texas. Prendergast says the survivors lucky — many of them were chased across the desert border into Chad by the Janjaweed.

"The Janjaweed are like a grotesque mixture of the mafia and the Ku Klux Klan," says Prendergast. "These guys have a racist ideology that sees the Arab population as the supreme population that would like to see the subjugation of non-Arab peoples. They're criminal racketeers that have been supported very directly by the government to wage the war against the people of Darfur."

Survivors say the attacks usually start at dawn, with bombs falling from planes of the Sudanese Air Force.

"And then here come the Janjaweed on camel or on horseback," Prendergast says. "They come rolling into the town, shooting and torching the village, often bringing women to the side and raping women indiscriminately. And in order to ensure that the destruction is complete, the government either sends ground forces to oversee the operation, or the attack helicopters, which often are the most deadly things."

"They arrived on horseback, killed my husband and took my son," says Toona, who still didn't know what happened to her son eight months later. She left Sudan with five surviving children after the Janjaweed burned her village.

"They never gave me a chance to talk to my child," Toona says. "Some of them dragged my son away, others slaughtered my husband, and some others took me to the side, and tortured me and left me there. My newborn was snatched off my back, and was left lying on the ground. I found him in that situation when they let me go."