Ansar Dine rebels have made a push southward from their strongholds in northern Mali. This week, they captured a town very close to the key city of Mopti. The fall of Mopti to the Islamist, al Qaeda inspired rebel group could be a huge disaster. For one, the city has a population of 100,000. It is also a central hub along the Niger river for transpiring humanitarian supplies for the entire region. If the supply chain is interruptued many hundreds of thousands of people will suffer. The fall of Mopti would demonstrate that Ansar Dine could move southward with impunity. All this lead to an emergency Security Council session last night, during which Mali formally requested military assistance from France. This morning Francois Hollande obliged. The scale of the intervention is unclear so far. But it is worth pointing out a few things: 1) This is an intervention. Not an invasion. Mali asked for help, and France is providing it. This is fully in line with international law. 2) Last month, the Security Council approved an African-led International Support Mission in Mali (AFISMA) to assist the Malian government in its fight against the rebels. But there were serious questions about the quality and readiness of the African-lead force. Phase 1 of this intervention was going to be mostly a training mission, which was to be accompanied by a political process to unify the government in Bamako and make amends with the less hard-line rebels. Then, the real fighting was to begin. It seems that the Ansar Dine has pushed up this timetable. 3) The Security Council was unified around the idea some kind of international military intervention was necessary (the disagreement was over the timing and other details). Even organizations like the International Crisis Group and Refugees International conceded that some sort of intervention was likely necessary. However, there were grave concerns that a poorly planned intervention would be worse than no intervention at all. What happens next is hard to predict. Presumably, the French forces are deployed to protect and prevent the fall of Mopti and its nearby towns. I would doubt that we’ll see an offensive operation heading too far north.