What should the United States do? Send five divisions and a coalition force?
If the people of Mali can't stop these armed fighters, then there really is no hope for UNESCO's heritage sites near the famous city of Timbuktu. I suppose there are people who think this version of al Qaeda is a threat, but, really, these are just separatist movements, of which Africa has many. If a country falls into failed state status and ends up being ruled by trucks filled with gunmen, then that's an issue for whom? Can someone unite Africa and create a credible mechanism to deal with these regional and internal issues?
I think this is largely something the locals will have to solve. No one can build your nation for you, and when it falls apart, it really is up to you. Save up and buy some gun trucks of your own.
The destruction of heritage sites is as old as can be. Carthage was once a heritage site, and look what became of it.