Story I just came up with about the earth

Humans find strange artifacts that point to a much greater old technology on earth. Of course we assume it is ancient aliens but eventually we find out that is in our ancestors, that we are the decedents of these great people and somehow lost our way. We then realize that we once had the technology to travel faster than light and we have a plan to get there. This is a story about a group of interconnected planets that are all filled with humans. They all have great technological advances and communicate and travel easily faster than light. Earth is one of those planets and somehow gets disconnected. The disconnection causes a great tragedy and earth takes millions of years to recover.