Leonidas decides that two Spartan cities are not enough, as he unveils his plans to expand his empire further than just the reaches of the Balkans. To the east, Alexios I Komenos of Byzantium decides it's best not to agitate the shirtless man with a massive spear and decides to head northward instead.
Alexios Komnenos will get a Golden Age every time a war starts. Given his position on the edge of the Great European Clusterfuck, he may be in a Golden Age for as long as he lives. His naval UU, a replacement for the Galleass, which heals 15 points per turn in a Golden Age is going to be healing quite a lot, I suspect. Sparta, likely to be a warmonger, on his western front, may induce him to expand east into Anatolia, and away from the bloodbath that shall emerge. Any significant expansion west would be a death sentence.