The mineral-rich east of the Democratic Republic of Congo has been dogged by conflict for more than 30 years, since the 1994 Rwandan genocide.
Numerous armed groups have competed with the central authorities for power and control of the potential fortune in this vast nation.
The instability has sucked in neighbouring countries to devastating effect – notoriously in the 1990s when two huge conflicts, dubbed Africa's World Wars, resulted in the deaths of millions of people.
What is happening in Goma?
After a rapid advance in the region, fighters from the M23 rebel group have taken control of most of Goma – a major city of more than a million people in the east of DR Congo.
Sitting on the border with Rwanda and the shores of Lake Kivu, it is a vital trading and transport hub that is within reach of mining towns supplying metals and minerals in high demand such as gold, tin and coltan, which is a key component of mobile phones and batteries for electric vehicles.
The rebels say they control the city, although there are still reported to be some pockets of resistance.
UN aid agencies have warned of a major humanitarian crisis with hospitals overwhelmed by casualties and bodies lying on the streets.
