When battles get quite large, you will find it relying more on CPU power than most games, so you may want to consider a more powerful processor if you’re building a new PC.
Generally speaking, Bannerlord is a medium level demanding game, with a lot of graphical options to tweak to improve the performance on your machine. Also be aware that as Bannerlord is still in early access, you will still probably experience FPS drops even on a powerful machine, until Taleworlds manage to iron out the causes and better optimize the game. It’s typical for publishers to understate the performance required to run their game, to encourage more people to buy it, so always take the minimum requirements with a pinch of salt.
Have a gander below to see the minimum and the recommended requirements for Mount & Blade II: Bannerlord on the PC (currently the only platform the game is available on).