PLEASE folks, nobody is talking about nations here, NF is a gameplay system used in V2 (and in EU3 maybe? I only played EU2). That system's implementation in CK2 in form of a "personal focus" is what we discuss here. Nobody has ever said anything about nations in CK2 time. I always think that people playing these games are mostly intelligent about history, if not always perfectly informed (as I am also not), and it hurts me when people assume others' ignorance without reading further than the title.
I believe you would agree that there were individual persons in the middle ages, who had some kind of control in the ways they make use of their time and energy, which at certain times could be directed at "focusing" on achieving certain goals. Yes? No nations. No national anythings. No.