In researching for my guide to the Gundam timelines and canon I took a look into the deep hole that is Dark History (or Black History, being the direct translation) from Turn A Gundam. Here reflects my findings, as limited as they are, as of April 2nd, 2020.
Huge, massive, thanks to Mecorx for translating this and dealing with my obscene obsession driven trying to map out the entire franchise.
Dark History as represented Turn X's Instruction Manual
The Master Grade Turn X, released in June 2014, has a small blurb on Dark History...
The translation is a follows,