Complex sentence: This home world was a key planet of one of the Commonwealth's member species, the genetically engineered Nietzscheans, who were displeased with the peace agreement and secretly attempted to usurp control of the Commonwealth.
Split into simpler sentences: This home world was a central planet of one of the Commonwealth's member species, the genetically engineered Nietzscheans. The Nietzscheans were displeased with the peace agreement and secretly attempted to usurp control of the Commonwealth.