Which battle saw Alexander defeat Darius III and become the de facto king of the Persian
Empire?

Battle of Gaugamela

Explanation:

The battle of Gugamela saw Alexander the Great face off against King Darius III in person for the second and last time. Alexander faced superior forces with his army heavily outnumbered but due to his superior tactics and army discipline, he defeated Darius III and inflicted such a blow on the Persian empire that they could not even hope to recover.

This battle ended with Darius III on the run and effectively made Alexander king of the Persian empire. Darius would later be killed by one of his own officials who was then executed by Alexander who had respected Darius.

answer; (b) ; /stronger bonds between the nations of africa