I actually love to read history books.
I would just look up channels like.
They seem to be pretty entertaining.
Depending what kind of story you try to tell different countries would be more interesting.
I am just gonna name drop different names and topics that in my opinion, are pretty interesting:
the crusaders, templars, the Jihad, the sicarii, the roman religion and their conflict with early christianity, people like Nero the emperor,
Janissaries. the Praetorian Guard.
These Guys from Assasins creed.
https://en.wikipedia.org/wiki/Order_of_Assassins
The Normans/ King Edward the first.
The Holy Roman empire, Egypt, Babylon, Assyria.
Hannibal, Flamma the gladiator, Alexander the great, Ceaser and Augustus/Octavius, Rasputin, Nikolai Alexandrovich Romanov.
These 2 channels talk about D&D lore and creatures.
They should have more than enough to pick your favourites from.
I also like to play games like heroes of might and magic, Age of Wonders etc.
Fantasy games use a lot of fantastical creatures.