Turtledove, Harry. "The Daimon"
Divergence: 415 BCE
What if: Socrates joined the Athenian attack on Syracuse, and in doing so ended up causing Alcibiades to remain at the head of the force despite his recall to Athens.
Summary: Alcibiades' triumphs over Syracuse and Sparta lead to a change, and focusing, of Athenian power and possibly to that of all Greece.
Comments: Analyzed in Michael Whitby's "Alcibiades, Syracuse, and 'What Next'".
Published: In Worlds that Weren't (ed. Laura Anne Gilman), q.v.; History Revisited: The Great Battles: Eminent Historians Take On the Great Works of Alternative History (eds. J. David Markham and Mike Resnick), q.v.; and Atlantis and Other Places, q.v.