From the BBC: "DR Congo violence: Panic in Goma as M23 rebels advance"

 Story here. Goma is in the far east of the Democratic Republic of the Congo, bordering with Rwanda. The city is economically important because of gold, tin, and coltin (columbite-tantalite which is refined to make tantalum) mines in the surrounding area. The city had been briefly captured by rebels in 2012, who later withdraw under international pressure and the deployment of UN "peace keepers" to the area. But the DRC has ordered foreign troops to leave, and now Tutsi rebels once more have surrounded the city and cut roads to the farms on which it relies for food. The DRC contends that the rebels are merely proxies for Rwanda, which is dominated by the Tutsi tribe and threatened to retaliate directly against Rwanda for attacks by M23. Although the situation is undoubtedly more complicated, on a very basic level it appears to be an ethnic conflict between the Tutsi and neighboring tribes. The article notes that 7 million people have been internally displaced due to this long-running conflict.