How did Alexander the Great bring cultures together?

He tried by establishing 70 Greek-style city-states, hoping Greek culture would be unifying, ignoring the fact that Greek cities were notorious for endless fighting amongst each other.

He married his senior Macedonians to Persian upper class women, hoping for a new unified breed of ruling class, but the Macedonians did not regard the progeny as equals.

He established Persian units within his army.

He promoted Greek language , but this persisted mainly at a commercial language.

Alexander died early and his generals divided his empire amongst themselves, forming separate kingdoms. The Hellenisation was superficial, confined to the ruling class - the remainder of the various peoples maintained their traditional cultures and languages.