In our universe, The Empire was greatly hurt by the Rebel victory at Endor, but by no means was it destroyed. The Emperor survived the attack on the second Death Star, (weather by grabbing something before landing in the reactor, or by jumping to a pre-planed clone body, is anyone's guess). The Empire is out to take back control of the galaxy, and at the same time is trying to keep itself together.
The Alliance, in our universe, was greatly buoyed by its victory at Endor. The Rebels took advantage of the Empires weakness and gained a substantial amount of territory. The Alliance is now trying to set up its own government in the territory it controls (the New Republic) as well as trying to fend off the Empire's efforts to crush it.
So now the Alliance, the Empire, and others duke it out while the Mercenaries (ever present) look on.