What if the Doric Invasion had moved further, even into Attica, and as a result butterflied Athens?
Some things I thought of off the top of my head; no Greco-Persian Wars most likely, the Attic Dorians would not have much love for the Ionians of Anatolia and would not protect them as easily. If they did fight it is most likely a victory for Persia. No Delian League, No Athenian Empire, No Peloponnesian War, more sea-faring Dorians (less Athenian domination and good location for the Attic Dorians to start growing a naval power base). No Alexander the Great. More Dorian Colonies (like Syracuse). Very different rise to power for Rome. Perhaps more phoenician power depending on the naval power the Attic Dorians and alt-Dorians in general have.