Complex sentence: The final rebellion to overthrow her is the main plot of the first three books, the anthology "Twilight of the empire" takes place in the time when Lionstone is strongest, shortly before the great rebellion.
Split into simpler sentences: The final rebellion to overthrow her is the main plot of the first three books. The anthology "Twilight of the empire" took place in the time when Lionstone was strongest, shortly before the great rebellion.