Niger is home to a longstanding insurgency.  The Tuareg are a nomadic people who live all across West and North Africa.  In Niger, they live in the north on the edge of the Sahara desert where they have lived for centuries.  These people have rebelled against the government of Niger on several occasions in 1916-1917, 1961-1964, 1990-1995 and the current rebellion which began in February of 2007 and is still ongoing.  There are distinct nuances to each of these rebellions and I am no expert and have not read up on all the facts but it seems that the undercurrent of the problem is that the Tuaregs have felt and still feel marginalized and, in some ways, exploited by the government.

If you want to read some recent news articles relating to this topic, see below:
FACTBOX-Uprisings by Tuareg rebels in Mali and Niger
2 killed in Tuareg attack in Niger
Areva is ‘nobody’s enemy’ in Niger after Tuareg rebel threats