For England, teachers are given a list of many topics to teach and they pick a few from the list to teach.
Here’s the KS3 History curriculum (ages 11 to 14)
Only the Holocaust is compulsory and even then Academies don’t have to teach it.
History is only compulsory up until 14. After that you have GCSE (14 to 16) and A Level (16 to 18) which are optional.
They take the same approach. Teachers are given a list of topics and they select a few from the list to teach.
This has its disadvantages. Someone may know loads about the Tudors but not anything about the Stuarts or vice versa.
How does it work in your country?