While Sudan insists it did not support the Chad rebels, people who have traveled through the border area contradict this. The U.S. also says Sudan is involved (without revealing its sources, which probably include satellite surveillance and agents on the ground.) Sudan apparently believes that, if the faction it backed got control of Chad, the Darfur rebels would have one less place to hide out in. But some of the Darfur rebels belong to tribes that have branches in both Sudan and Chad. That said, Sudan's brutal policy in Darfur doesn't make sense either, but there it is. The Sudanese leadership are ruthless, and don't much care how much mess and misery they create.
April 22, 2006: The African Union has sent a team to investigate the charge that Sudan backed the Chad rebels. All the evidence points to Sudan's guilt. But Sudan treats the African Union with barely disguised scorn, and won't bother much with another accusation from them.
April 21, 2006: Gunrunners are doing a booming business with the government, with additional weapons being flown and trucked in each week. Some of the deliveries are pretty visible, like the six Mi-17 helicopters that recently arrived. These cost about $5 million each. More and more of Chad's oil revenues are going to the arms suppliers, who usually demand cash up front.
April 20, 2006: France is sending another company (150 men) of troops to Chad, where there are already 1200 French soldiers and airmen. The French troops will help the Chad government resist Sudanese backed rebels. Previously, the French troops were told not to interfere, as Chadian rebels do have a legitimate complaint against president Deby, who has bent the rules to run for a third term next month, and is considered corrupt and autocratic.
April 16, 2006: The government demanded $100 million from the oil companies running oil operations in Chad. This is money the government agreed to put aside for economic development. But president Deby needs the money to stay in power (buy weapons, bribe allies, and so on). Deby threatens to halt oil shipments if the oil companies do not produce the money immediately. Chad also withdrew from the peace talks trying to settle the rebellion in Darfur. This is considered an empty threat, as the government needs the revenues it is getting.
April 15, 2006: Some 15,000 refugees fled across the border into Sudan, to escape the fighting with rebels. The fighting itself had died down, with about 400 dead (mostly rebels) on the frontier, and in the capital. Some 200 rebels were captured. The rebels had withdrawn to their bases in Sudan. Their attempt to make a run for the capital and trigger a larger uprising against president Deby, had failed. This sort of thing sometimes works in Chad, but not this time.
April 14, 2006: Soldiers and police killed or captured the several hundred rebels that drove into the capital. The captured FUC rebels admitted they had received support from Sudan, even as the Sudanese government insists it had nothing to do with the incident.
Diplomatic relations with Sudan were cut and a state of war declared. Chad closed its border with Sudan, as did the Central African Republic. This doesn't mean much to the Sudanese militias, that can easily cross the borders elsewhere. There are only a few official border crossings (on the few roads), and not many border patrols.