Those three areas are:
1. The history of the British Isles
2. The history of the Jews, and
3. The history of World War II
Each area has attracted remarkable talent, mostly in English I should add, and you can always read yet another great book in these areas, even if you already have consumed many stellar offerings.
Whether you should double down in these areas, or strike out and diversify into the many other areas with lower quality expected return, is in fact a key question when it comes to how to read.
(Of course, a small number of books cover all three areas, though I would not suggest that they get triple credit.)
Are there any other such areas I am missing? Somehow American history does not do it for me — too much stupidity, repetition, and needlessly “clampdown patriotic” perspectives.