Evidence is building that the Jedi fell to the dark side 200 years before the Star Wars prequel trilogy. When Qui-Gon Jinn discovered Anakin Skywalker on Tatooine, he recognized the possibility Anakin was the fulfillment of the Chosen One prophecy. Although the Chosen One was mentioned many times in the prequels, the text was only revealed in Claudia Gray's novel Master & Apprentice back in 2019. "A Chosen One shall come," some ancient prophet foretold, "Born of no father, and through him will ultimate balance in the Force be restored."
The text raises as many questions as it offers answers. It's still unclear, for example, exactly what "ultimate balance" really looks like – especially in light of Palpatine's resurrection in the sequel trilogy. The use of the word "restored" is also significant, because it implies a previous state of balance that has been lost. But when exactly did the Force go out of balance in the first place? Star Wars is gradually beginning to answer that particular question, through Lucasfilm's Star Wars: The High Republic transmedia initiative.