If I may offer my advice as a Forgotten Realms Lore Monkey... >.>'
Amn would be the Venice/Spain of Faerun, Tethyr is like France, Lusken was kind of like Denmark or Novgorod, I think Cormyr was like medieval Britain, Calimshan is like Egypt...Waterdeep might have been like a Constantinople in terms of multicultural aspects and their trade networks.
Mulhorand is like ancient egypt, same gods and everything. Halruaa is sort of like Italy and France.
That's all I can think of at the moment, Also, the Zhentarim were more of an underground organization then a country. Although they did control a few towns and castles...