Bosnia and Herzegovina
The track is represented by the circles superimposed on the Gorgoroth region on the map; not that the circles are not actually considered to be part of that region.
That's from CE Rulebook.
The Nazgûl Strike! (C)
Play if the Fellowship is on step 1 or
higher on the Fellowship Track.
Move any or all of the Nazgûl.
Then, if at least one Nazgûl is in the region
with the Ring-bearers, you may
either discard one Free Peoples Character
Event card from the table or roll for
the Hunt (as if the Free Peoples player
had moved the Fellowship).
First, they can't enter the same region (stated in the rule above). Second problem that comes to my mind is about moving Nazguls - Play if the Fellowship is on step 1 or higher on the Fellowship Track. I don't see it happening in Mordor.