TMI = Too much information...
I have edited books where all of the history of mankind have been recorded and the book is about submarines. I don't need that much information!
Use the details you have gleaned from your research judiciously. Just because you have all the detail doesn’t mean you will write it all. The goal is to enhance the reader’s experience of the story and to help him/her imagine the world in which he/she will be traveling, not to teach a history course. Strike a delicate balance between too little description of the world and too much description because either extreme will alienate your reader.
Too much detail or backstory. Many writers fall into the trap of adding too much detail or description. "Describing the color and length of a protagonist's hair is great if it's relevant; otherwise it's fluff you can cut," says Don Muchow of Would That It Were. Diane Walton of ON SPEC deplores "long exposition 'lumps' that stop the action dead in its tracks, so one character can explain to another that their society has been operating in a certain way for centuries, or the long speech where the bad guy explains why he has to kill the good guy."