Actually that's a historical time period. The reason it's nicknamed that is because of the book written about the time period which is called that. So you aren't lifting anything from another story, they're factual events that belong to no one.
Well, while I will not state quite so categorically that we won't base a realm theming off of any historical period, I certainly have no intention to do so.
BattleMaster is not this world. Nor is it Middle Earth, Westeros, Scadrial, Velgarth, Midkemia, Thedas, Kenor, or any other world from any other story, franchise, or history.
BattleMaster is BattleMaster, and it has plenty of its
own history.