Complex sentence: The term "Galactic Empire" appears at the end of the novel, indicating a possible link to the Empire Series, of which the first novel, "Pebble in the Sky", was written in 1947, the year before "Mother Earth".
Split into simpler sentences: The term "Galactic Empire" appears at the end of the novel. The first Empire novel, "Pebble in the Sky", was written in 1947, the year before "Mother Earth".