From the post:
Heavily inspired by the characters and events of Rogue One, Rise of the Empire carries us back to one of the galaxy's darkest hours. And while the expansion's rules may grant you a better appreciation for how you'll wage your conflicts in this new chapter of the Galactic Civil War, they simply cannot illustrate the full scope of your upcoming struggles.
The Republic is no more. The last remnants of the Senate have been swept away. In their place, the Galactic Empire looms across the galaxy. Palpatine, its tyrannical, self-appointed Emperor, exerts his will via Star Destroyers, Stormtroopers, and TIE squadrons. These machines of war inspire fear and keep the local systems in line.
Still, all hope is not lost. Even under the crushing weight of Imperial oppression, small bands of insurgents have come together to form a fledgling Rebel Alliance. Driven by little more than their dreams and ideals, these brave freedom fighters risk their lives on daring secret missions and surgical military strikes. Bit by bit, they hope to chip away at the Empire's aura of invincibility and inspire the galaxy to open rebellion.