Why did the songhai empire come to a end

In 1590, al-Mansur took advantage of the recent civil strife in the empire and sent an army under the command of Judar Pasha to conquer the Songhai and to gain control of the Trans-Saharan trade routes. After the disastrous defeat at the Battle of Tondibi (1591), the Songhai Empire collapsed.

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answer; /// i believe that the correct answer is (d)the huang he river valley;