Here’s scenario I spun a while back on the Constructed Languages list serve:
Philip of Macedon isn’t assassinated. As Hegemon of the League of Corinth, he invades the Achaemenid Empire. Under the command of Alexander, the invasion is successful.
Philip then does what’s worked for him before: redistribute seized land and wealth (esp. gold) to his favored men. Of course to keep his allies sweet, Philip has to seize more gold and land and so on. His empire must always expand.
Because of the nature of his cavalry/phalanx army, expansion works best in flat areas with lots of gold. That means Egypt is next after Persia, then Iberia. Italy is neither flat nor wealthy, and so Philip ignores it except to use the southern tip as a staging area for the Iberian campaign. In the long run, this will have the amusing result of Hellenic languages spoken everywhere but northern Italy, where there is a strange Indo-European isolate, somewhat similar to the Celtic languages…
Anyway, upon Philip’s eventual death, Alexander inherits an empire including OTL Turkey and Iran, northern Egypt, Albania and Croatia (at least the coasts) Crete, Corsica, Sardinia, southern Italy, southern France, and most of Iberia. This will be the core Hellenic Empire, and the future home of the Hellenic Language Family. There are also Greek outposts scattered across the northern coast of Africa and the Atlantic coasts of Africa and Iberia.
The empire is run according to Aristotelian principles, where the basic political unit is the polis and the citizen is a land-holding man who can equip a cavalry officer and infantry brigade. Different poli are run differently, but generally have three counterbalancing groups of hereditary royals, rotating generals, and elders voted in by the wealthy families. The economic system is mostly concerned with the manufacture and hording of treasure.
The people on top speak Athenian Greek in public and Macedonian or Thesselian at home. Thracian, Illyrian, and Paeonian mercenaries are all over the place, and most scribes and low-level bureaucrats speak Persian or Egyptian (there’s quite a bit of competition there). Non-Greeks are generally slaves. Over time, these slaves are more likely to be owned by the polis, rather than individual citizens, and rented out for whatever purpose.
It’s not a stable system. Problems in the 100s BC include black-market gold, ambitious local governors, wealth concentration (in the form of gold and slaves), revolting slaves, and the Phoenicians, who are sitting the rest of the Mediterranean’s wealth. There is a push to conquer the lands around the Danube and Alps, but for now, the lack of a stable land route between Anatolia and Iberia divides the empire culturally into east and west, with the east further divided into Persian-influenced Anatolia, Egyptian-Influenced Africa, and Core Greece. It seems like the only thing that will keep the empire together would be a common enemy.