Abil Musa, 15, a Nuba cattle herder, on the outskirts of Kadugli, Sudan. Moises Saman/Magnum for The New York Times

The war in Sudan, which has been raging over a year, has killed many thousands of people and displaced millions more. Despite that, the brutal civil conflict has remained nearly unknown to most of the world.

My colleague Nick Casey traveled to Sudan and spent time with an elusive mountain army that has built its own state within a state — a vision of what the nation could become.