EDIT: Here is what is inscribed upon the Stone of Alliance
The Great People of Aostra and Aisonia agree to work together for the glory of All Greeks.
Aisonia is given Sovereignty westward to the Balkan Spine, and northward to the passes of Macedonia, thus Aisonia promises to protect these funnels into Greece, and protect the Grecian people from barbarians.
Aostra will bring culture and bronze to Aisonia, and recuits for their wars and trade for their merchants.
Together, from the Northern Mountains to the Southern Seas, Greece will stand between them.
Hey.
This will fit the backstory. The Stone of Alliance is the reason how the bronze age culture got so far north, and he storm that devastated your island would have ended the trade of this bronze, which leads directly to furthur wars.
Just checking to see if you are ok with the wording of that in the backstory.