Mountain gorillas exist only in three countries: Rwanda, the Democratic Republic of the Congo, and Uganda. As dangerous as the Congo is, most people trek in Rwanda and Uganda. The only Rwandan location is in Volcanoes National Park on the northwestern border of Rwanda. It is part of Virunga, which is shared with the Congo. That being said, the gorillas do sometimes wander into the Congo, but they often stay on the Rwandan side.
While the Congo side is filled with trappers and poachers and civil unrest, the Rwandan side is peaceful with trackers and researchers who study, protect, and care for the gorillas. Somehow the gorillas seem to know this, and so rarely venture into the Congo.