Simplify the following text for a Grade 12 native English-speaking person.
Original: The characters occasionally refer to `` Earth-that-was '' , and the film establishes that , long before the events in the series , a large population had emigrated from Earth to a new star system in generation ships : `` Earth-that-was could no longer sustain our numbers , we were so many . ''
Simplified: The characters refer to `` Earth-that-was '' and in the movie , it is said that long before the events in the series a large population had left from Earth to a new star system : `` Earth that was could no longer sustain our numbers , we were so many . ''