Final answer:
The Mali Empire declined due to internal strife, external attacks, and the opening of maritime trade routes by the Portuguese which rerouted commerce and diminished Mali's trading power.
Step-by-step explanation:
Decline of the Mali Empire and the Opening of New Trade Routes
Trade routes bypassing the Mali Empire, particularly those utilised by the Portuguese along the Atlantic coast, significantly contributed to the empire's decline. Malian control over lucrative trade, especially in gold and salt, was weakened due to internal strife, external attacks, and new competing powers like the Songhai Empire. These factors, coupled with Portuguese arrival in the 15th century, gradually shifted commerce away from Mali's trans-Saharan routes, leading to an economic and political downfall.