The fact that the government is divided into three branches is known as the "division of power" - the power is distributed to avoid power abuse, so that no instance has unlimited power.
The fact that the three branches are overlapping is known as "checks and balances" - the branches check the other ones (whether their function is lawful) and balance each other.
Just compare a river map of West Africa to a map of West African kingdoms.
You can clearly see that all of these kingdoms form around the Niger River.
More support to this: None of these other rivers are even in Africa: The Thames is in England, the Indus is in Pakistan, and the Euphrates runs through the Middle East.
