It's what's left of the Empire. They ran off and created a bigger Death Star. This one was called Starkiller, and they used an entire sun to power it. Wiped out an entire system. It didn't have to be within range, it could fire light years away.
Things were good once we managed to get them to sign the concordance. Seemed to go back to peace times. Mon Mothma dissolved the chancellor's wartime powers, we cycled our capitol government to different planets rather than Coruscant to show that we were all one people, and get the people to trust the new Republic.
And yes, he did. You were training him, along with many others, and he and his knights turned on you and killed everyone. I can't understand how you must have felt, but I don't blame you for leaving.