Malphaestus
Touched by the Apocalypse
I like oros. A lot. Although I do have some ideas about the Estogan rebellion. After the Estogans forced the Orosians off their island, they began to build a navy, and called out their magic users, the mysterious Tidecallers. The Estogans lured the Orosian counter-invasion fleet to the rocky northern shore, where the Tidecallers dragged a large chunk of the fleet into the cliffside. The remnants being torn to shreds by the Estogan vessels. Using Orosian tech and their own know-how, their navy continued to grow.
After this battle, the Estogans would push the Orosians back, winning victory after victory on the seas, until the Orosians dared not leave port. Seizing the Orosian oil convoys from the West, Estoga was able to force Oros to accept a peace, granting Estoga independence. Ever since, the navy has only improved, as the Estogans are determined to never be humiliated like that again.
Plus, losing a fight might wound your pride enough to cause more interesting drama.
Oros had to lose one way or another for you to be freed, I like the way you portrayed this option though. It reveals just how crucial the oil imports are to the nation. Still, I have also hidden a few other ways to cripple the Empire, maybe even overthrow it, in my CS.