If you want to play with these ideas a little, the excellent game Crusader Kings 2 (https://www.paradoxplaza.com/crusader-kings-ii/CKCK02GSK-MAS...) has a $5 DLC called Sunset Invasion that's worth picking up. It causes your session playing through 700 years of medieval European history to be interrupted at a random point by an cross-Atlantic invasion of Aztec conquistadors, who bring with them their own religion and strange new diseases.

The game disables this invasion by default, so you don't have to worry about it wrenching your playthrough in weird new directions unless you want it to. But it's a fun little way to shake up the usual with a bit of alternate history.