The conventional wisdom is that Sparta won, because Athens ultimately surrendered and faced total destruction.

But as Robert Strassler points out in his epilogue to the Landmark edition, which I read this time, the big winner was not a belligerent. Rather, victory belonged to an observer, Persia, which stood on the sidelines and encouraged the fight, and then moved in to collect its winnings. I think too often we don't consider that as an outcome in wars.