Why are sub saharan rivers not very useful for travel?

The reason is because "many don't link to the ocean and have many waterfalls".

From geographical point of view the Sub-Saharan Africa is the zone of Africa that is situated south of the Sahara. Politically, it comprises of every single African nation that are completely or incompletely found south of the Sahara. It contrasts from North Africa, which is viewed as a piece of the Arab world.

answer; the confederacy could afford to move a large number of prisoners hundreds of miles but could not afford to fee and house the prisoners;

answer; (b) capitalism;