Complex sentence: The series is set with a space opera theme, in a distant future where mysterious alien benefactors have helped Humanity spread out among the stars, colonizing a number of planets in the Spiral Arm of the Milky Way galaxy.
Split into simpler sentences: The series is set with a space opera theme, in a distant future. Humanity has spread out among the stars, colonizing a number of planets in the Spiral Arm of the Milky Way galaxy.