I mention decline a lot on here, in passing, as in decline of the western empire. But I don't feel I have a good grasp of the history of empires more generally (well, things that have gotten that label in history, like the roman empire).
And I don't want to end up in bougie land trying to learn more about it, cause I figure they're going to romanticize empires more so.
There are some good works on ProleWiki you could find.
Absolutely, the smallest, most niche topic you can think of, there may just be a good bit of info on it on ProleWiki.