Complex sentence: It was run by a single government called the Ruling Council and there was no need for a police force until an alien race called the Manhawks, who instigate the practice of stealing for the thrill of it, invaded.
Split into simpler sentences: It was run by a single government called the Ruling Council and there wasn't any need for a police force. That is until an alien race called the Manhawks, who instigate the practice of stealing for the thrill of it, invaded.