Gods Before Us

Earth has been invaded. But this invasion wasn't something we'd written about. No alien ships. No scary monsters. No threat to our entire existence, an existence that could have been ended in an instant. This invasion was slow, deliberate, methodical. Why? Who would spend decades setting up the invasion of a species on another planet if they had the power to simply wipe them out? They didn't come for resources. They didn't come for slaves. Then why did they come? Why?