It isn't a case of using rules. Think about the meaning. Since he wanted to control that area - it was one area - his potential empire. How would you split it into different 'areas'? He wanted to control the entirety of the area - he wanted to control all the area. Perhaps the missing 'of' is what is confusing? I want to eat all the apple. I don't only want half. The spilt drink covered all the table. You would only use 'areas' in that sentence if it was clear what the individual areas you were referring to were.

Nice question no really just habit plzz tall me r/ w