Posted this before. Worth mentioning this again.
For those not old enough to remember the Realms when it was first released. The entire idea of it was that it was a world with connections to our own. A lot of the myths, legends, and gods bled into our own. But that connection was forgotten in modern times.....hence the "Forgotten" Realms. The idea was that Elminster still made trips to visit Ed and provide him with tales and lore about The Realms. Ed was just the "conduit" for Elminster.
So some similarity between FR and our world was intentional. But TSR and WoTC brought in people who added to the Realms with more explicit clones of real world cultures. Ed had literally zero control over this.
Mulhorand (ISBN 0-88038-821-8), was chiefly developed by Scott Bennie, who wrote:
Mulhorand was created by Ed as their land of origin. When TSR Inc. hired me in 1989 to write of those lands, I was told to base them on the ancient earth empires of Egypt, Babylonia, and Greece. I did the work according to the specs I was given, though I twisted them to reflect their antiquity, whittled down the vast pantheons to reflect their decline.
Ed has since gone on record numerous times stating that the printed versions of the Old Empires and many real world rips were straight up out of his control.
The Horde (ISBN 0-88038-868-4) was made entirely by David Zeb Cook, who also had a hand in Kara-Tur. Again not Ed Greenwood.
The Gur, were created for the Heroes Lorebook (p. 60. ISBN 0-7869-0412-7.) by Dale Donovan and Paul Culotta and expanded on by Troy Denning, and Dave Gross.