The Mali Empire began to decline in the 14th century due to a combination of factors, including internal strife, economic difficulties, and external pressures. One significant factor was the loss of control over key cities like Gao, which was a critical hub for trade and military strategy.
The empire faced challenges from rising powers, including Songhai, which eventually took control of the important trading city of Gao and other territories. This shift in power dynamics, along with the weakening of central authority and the eventual fragmentation of the empire into smaller states, contributed to the decline of the Mali Empire.
It's important to clarify that the options you've listed contain some inaccuracies. For instance, the Mali Empire was not conquered by Axum, and Ghana did not take over its territory; instead, the Kingdom of Songhai rose to prominence after Mali's decline. Additionally, Mansa Musa was not captured by Sundiata, as Sundiata Keita was the founder of the Mali Empire, and Mansa Musa came to power much later.
Overall, the decline of the Mali Empire was a complex process involving the loss of territorial control, internal divisions, and the rise of rival states.