I haven’t seen The Last Jedi yet, but, no, the Empire wasn’t soundly defeated in Return of the Jedi. The top two figureheads were killed, but that alone doesn’t mean utter defeat then and there.
In The Force Awakens, it’s pretty clear that:
1. There’s a new Republic
2. The First Order grew from the ashes of the old Empire
3. The Republic doesn’t believe that the First Order is a credible threat
4. The Resistance - led by Leia, who has seen this shit before - is a splinter group, mostly operating without Republic approval
5. The seat of the Republic’s government, with presumably most of its leadership, was taken out by Starkiller Base
6. Ultimately, things are going down a familiar path because too many people refuse to learn from history
In The Force Awakens, it’s pretty clear that:
1. There’s a new Republic
2. The First Order grew from the ashes of the old Empire
3. The Republic doesn’t believe that the First Order is a credible threat
4. The Resistance - led by Leia, who has seen this shit before - is a splinter group, mostly operating without Republic approval
5. The seat of the Republic’s government, with presumably most of its leadership, was taken out by Starkiller Base
6. Ultimately, things are going down a familiar path because too many people refuse to learn from history
