Five years after Princess Luna left and formed the New Lunar Republic, the Republic has become caught in a war with the Solar Empire. After making a comeback, the Republic decides to try the impossible and convince the Mane 6. But even if they can, it's still a longshot that they can win the war.
The Solar Empire is no longer controlled by Celestia. Her lords took control after seeing a weakness, and have caused terror and death throughout the world in Celestia's name.
Celestia, meanwhile, has created the army within the army, Celestia's Army. However, a strange obsession prevents her from acting against the Empire.