BetaSpectre, to be honest, I've had similar associations. At vanilla game countries tend to come out of the project, but... the Gate...
The first association that the aliens had transdimensional teleportation technology. Moreover, there are indirect indications on it in the setting (Iron Tribe main city etc).
What about other cities...
Forbidden Caverns is associated with alien base from Enemy Unknown/Within. There were massive caverns with platforms hanging over the void. By the way, it would be very interesting to speculate what exactly happened at GHOSTGATE region.
Halls of Madness... maybe a kind of alien Hypno-Devices "Disneyland" for loyal collaborators from the Sirius Cult?
Nightspyre... it reminds City-17 Citadel from HL2. And Dark Eldars Comorragh, you know where it from.
The "hope" and "despair" sounds situable for Dominion's dark cult, but the Tower of Souls? Probably, it's a "psychoactive" place with powerful psi-radiation level and, most likely, with a specific source of such radiation. And perhaps this is a kind of Hall of Fame, where "lives" holographic images of the fallen heroes, or something like that.