I've been meaning to do this for a long time. Anyway, a few notes on Ghana, Mali and Songhay from From Slavery to Freedom: A History of African Americans by John Hope Franklin and Alfred A. Moss, Jr. Hopefully these will be expanded as I get more time to organize them. Let's start with Ghana.
The Classical West African Kingdom of Ghana sprang up about 500 miles from what we now know as Ghana. The kingdom was also known by the name of its capital city, Kumbi Saleh. Ghana's written history extends back to the 7th century but evidence exists that suggests the kingdom's political, social and cultural institutions extends to the very early Common Era.
Ghana began as an unbounded collection of settlements. The people of the early Ghanaian kingdom were skilled farmers but the area was often plagued by droughts which eventually led to the desert being extended into their farmlands. As such, a booming trade economy grew out of Kumbi Saleh which soon became an important commercial city during the Middle Ages.
As the influence of Islam spread, Ghanaians adapted and by the early tenth century there was a Muslim area in Kumbi Saleh and people across the kingdom began to gradually accept Islam. With the spread of Islam, Ghana's power grew and so did the kingdom's prosperity. By the eleventh century the king of Ghana had adopted Islam and Ghana's army had grown. Trade routes extended across the desert, bringing wheat, sugar and fruit from Muslim countries along with textiles, brass, pearls and salt in exchange for Ghanaian ivory and gold.
With the rule of the Sisse Dynasty, Ghana reached the apex of its influence. Beginning in 1062 Tenkamenin took over as ruler of the prosperous kingdom. Tenkamenin headed a religion based on the belief that every object contained good and evil spirits which must be satiated to ensure the continuing prosperity of the people of Ghana and of the kingdom itself.
In 1076, the Almoravids, a band of Muslims, invaded and seized the capital of Ghana, bringing the city under its religion and rule. The invasion caused strife across the kingdom and soon droughts diminished the flourishing economy. Under these circumstances, Ghana weakened and fell to wave after wave of conquerors in the 12th and 13th centuries, leading to the kingdom's ultimate destruction.