These treaties do not necessarily entail joining war efforts of one or the other treaty signatory nation; terms of defence agreements could include anything from joint military exercises for training purposes, exchange knowledge, info/intel, etc. and don't usually reflect an 'aggressive' nature but more on the defensive.
I won't be surprised to learn that Belgium too has signed cooperations of this nature with a few countries not only in Africa but also in Asia.
If it's true that Pres Sarkozy has promised to make public the defence cooperations France signs with other nations, that's a good step forward. I believe the French people have a right to know, scrutinize and ask questions, have a say about the treaties that the French govt signs with other nations.