In the last week, Chadian border troops, Sudanese refugees and Chadian villagers came under attack by hundreds of armed Sudanese tribesmen. The armed Sudanese belonged to  one of the Sudanese government backed Arab militias organized to drive black Sudanese tribes from their farming and grazing lands, so that the Arab tribes could occupy the land. There were several dozen casualties. Over 100,000 of the displaced Sudanese have fled into thinly populated northeastern Chad. This are does not have many people because there's not much water. There is plenty of sand and heat. Sudan has promised to work with Chad to prevent such incursions in the future. It is thought that the Sudanese militias were armed by the Sudanese government, and then just turned loose on their black Sudanese neighbors. When the Sudanese government says it does not control the militias, there's quite a bit of truth to that.