[Epona]

Just to add that Alexander didn't even replace other cultures with his own culture, but a bastardized version of Classical Athenian which he attempted to adopt but then warped it beyond recognition.

The man was an intense egotist - he commissioned loads of busts of himself - the first time realistic portraiture appeared in Western art (I say Western only because I don't know for sure about the rest of the world) - he claimed to be a god - yet said he walked in the footsteps of men such as Perikles, who would have thought him an abomination to everything they believed in.

If you're in any doubt as to the destruction of pre-existing cultures by Alexander, just look at how far Hellenistic (as opposed to Hellenic) architecture spread during that period. It can be found from Athens and Italy to Persepolis. Each new city founded (many called Alexandria) was pretty much a clone of the last, built upon the ashes of the old culture.