I just recently completed my second playthrough of the game, paying more attention to the cultures of the previous golden age, so this first part will be about them.
On Ancient WeyardFrom what I can come up with there are the Jenei, Exathi, Fori, Beastmen
The Jenei can be subdivided into various groups, some speculation here, including the Neox, the various clans (Mercury in Imil, Mars in Prox, Umbra, etc) Ankohl, and more than likely some others that havent been though of yet.
Of the clans, I think can be said that they were left as stewards from the previous Golden Age to watch over the lighthouses while the rest of the Jenei population dwindled. I personally think that the Umbra clan was an offshoot of the Neox that pushed towards the mastery of light and darkness, and consequently the sealing of Alchemy to stop them.
The Exathi as described in the game were master craftsmen. We are presented with three cultures from these decendents.
Those at Passaj, master smiths and armorers. Those at Ayuthay, master masons. And lastly, those at Port Rago, master shipwrights. There are probably others around Weyard that will be in the fourth game.
The Fori are the simple folk, not much is said about them except that there was nothing special about them, hence them being called simple folk.
The Beastmen are the group that most people dont like. (I think the idea of having an entire race of furries is a bit off, but this was made in Japan, pardon the prejudice) At first I was completely against it, then I started thinking about them similar to those at Garoh. It stuck for a while, but it still didn't seem right. The beastmen seem fundementally different from the lycanthropes in that, the beastmen are fully fledged beasts changed, or humans that reverted to a more beastial form, due to the release of alchemy during the Golden Sun Event. The people of Garoh can only change into werewolves during the full moon. So with that idea gone, I finally realized that oddly enough, having an entire race of beastmen does fit. Imagine people with heightened scenes, like Wolverine (The guy from X Men), except an entire race of them. They are all more like superhumans, with a furry side effect. They have psyneregy, but from whats seen in DD, its more nature based than raw power. They are the ones that did most of the construction of the Apollo lense, while the Jenei were the designers, as no doubt they were for every alchemy machine.
A little bit more on the Umbra Clan. While at the Apollo Lens, I noticed that someone said something along the lines of "Where is it pointed, at Tuaparang or Mt Aleph?" (Despite what it looks like, that is not a direct quote) I took that as, Tuaparang is nearby Mt Aleph. I think that when the Golden Sun was lit, it released more than just alchemy. I think it may also have unlocked or led to Alex unlocking the prison for the Umbra Clan, and consequently reviving them. Does it really make sence though that the prison for those that tried to take over Ancient Weyard was also under the place of the core of alchemy? It may also be the reason why the psynergy vortecies are all located nearby Mt Aleph. As is evident in the Konpa Ruins, the Tuaparang are the ones behind them using their machines, though some may occur naturally.
"Modern Cultures of Weyard"This part will be about the influences, geography, and some etymology of Angaran Cultures.

Go to
http://www.gs-adeptsrefuge.com/dd/images/worldmap.jpg for the DD map, I'd post it here but its massive
Okay, I'm going to have to shift the GS1 map around a little bit, because some things were there in Dark Dawn that should have been there in GS1 that weren't
The places I believe were there prior to the Golden Sun Event (GSE) are, Konpa, Harapa, Passaj, Ayuthay, Craggy Peak Ruins, Teppe Ruins, Belinsk, Port Rago, and The Endless Wall.
Where I believe these places would have been are:
* Konpa, just underneath the first bridge that Master Hammet crossed over when he left vault on the small strip of land. As the GSE remolded the land, the Bilibin Mountain Range would have closed with the range north of Kalay, crushing it in the center and making it the only pass north and south. (Besides the pass at Carver's Camp which appears to have opened with the GSE)
* Harapa, would have been in the mountains almost directly south of Kalay. During or shortly after the GSE, the mountains flattened out pushing northern Gondowan further south, opening up the Karagol Sea to the Eastern Ocean. I believe that this is where the earthquake diverted its path pushing Kalay further west to the other side of that mountain range, because its clearly not accessible in DD, but it does still exist.
* Passaj, in the mountain range of the southern part of the Lamakan Desert, which when pushed up to become to snowy area would have dropped Passaj right where it needed to be, while the rest of the range continued to move north leaving Craggy Peak at the appropriate location.
* Ayuthay, on the small peninsula, southeast of Kalay. Pushed down forming a larger peninsula during the GSE.
* Craggy Peak Ruins, as stated in the Passaj post, in the southern central part of the Lamakan mountain range.
* Teppe Ruins, placed in the northern Lamakan range, one of the reasons its suffering so badly is due to the sudden change from such an arid climate to one freezing in a high altitude.
* Belinsk, this one is tricky, I would place it's ruins just east of Bilibin, on one of those outstretches of land, like Harapa, I think once the beastmen grouped up, and the Fang Tribe became the established leadership, they moved fast, rebuilding much of Belinsk while polishing up a lot of what was already there.
* Port Rago, I dont think much happened with this other than that it was just not mentioned in GS1&2. I'd place it on the far eastern edge of Angara, somewhat north.
* The Endless Wall, surprisingly flexible, placed mostly on the northern Lamakan range, managed to shift during the GSE without much damage done.
More to come in this section but I need a break