Cibola is a relatively recent addition to the Golden Circle, and it's role is still a bit tenuous. Originally discovered as a source of spices and gold, Amber was not even originally aware of the presence of the Cibolese. This accidental invasion could have easily ended in bloodshed, but Cibola showed surprising (some who know them now say uncharacteristic) restraint, and a peaceful settlement was reached. Cibola had resources aplenty, and the prospects of trade were tempting indeed.
Since then, Cibola has been a solid ally of Amber, though the same cannot be said for the rest of the Golden Circle. When the shadowpath was first opened up, Cibolans spilled out to explore these new worlds, and made few friends with their bloody habits and arrogant demeanors. Cibolan agents have been found or suspected in every shadow connected to Amber, always looking for places of power and sources of magic, often destroying or stealing valuable cultural artifacts in the process. For all that this has made them few friends, they have been very careful to never cross Amber directly, and when a matter has reached a point where Amber must intervene, Cibola is always happy to show what a good ally it is, slaughtering entire families of those who Amber calls to task, and sending their flayed skins as a sign of respect.
Cibola is hundreds of miles of thick jungle, much of it virtually impassable. The heart of the Cibolan empire is somewhere deep inland, among the mountains, but the only route to it is a single road from the port city of Antukt that goes hundreds of miles through the jungle. Visitors are not welcome inland, and when most Amberites think of Cibola, they think of Antukt, the coastal city of riches, surrounded by jungles.
The coast itself is long, and there are a few settlements or places of interest among them. The most famous of these to Amber is Garn's Folly, the first landing place of the expedition from Amber who found this place. It's abandoned these days, and the jungle has reclaimed it, but the shape of the buildings can still be made out, as well as the remnant of the old docks. A little bit north of that is black sands, a salt lagoon held by house De Sorgo of Amber.
Natural resources abound in Cibola, most notably the fruits of the jungle. Anythign that can be harvested from a plant can be found in Cibola, and they export fruits, spices, rubber and a variety of medicines and drugs, not all of which are necessarily legal in Amber. They also seem to have an abundance of soft metals - gold, silver and copper - and excel in their working. Lastly, Cibola excels at weaving and clothwork of every stripe.
Cibola buys a great deal of iron, worked and raw, and also hardwoods. While there is always some luxury trade, Cibola seems most interested in making up for gap in their own capabilities. This includes manpower and knowledge, and Cibola is a known market for slaves. The sole exception to this rationality is new fabrics. Fabrics - especially the raw material for those fabrics - which the Cibolans are unfamiliar with can be sold for a king's ransom to the right buyer.
Cibola's navy is distinctive in that they still use galleys. While they are adequate sailors, they are fearsome in battle at sea. Once engaged, the black galleys of Cibola are not dependent upon the wind, and the drug induced battle haze the rowers are brought to makes them superhumanly fast for short distances. COmbined with heavy boats designed for ramming, a Cibolan galley can split most ships in half, barely slowing down to do so. This battle haze can only be maintained for so long, and is poorly suited to attack, but it means that Cibolans ships are rarely troubled along the shadowpaths.
The creative use of pharmaceuticals is not limited to the navy, and the troops that have been seen in the Golden Circle, usually offered to Amber's service, tend to be drug-addled zealots, lookign to die in battle, or to bathe in the blood of their enemies. They are very disturbing on the battlefield to both friend and foe alike, and despite Cibola's cheerful, enthusiastic willingness to send any number of troops to die under the banner of Amber, they are only taken up on this offer under the direst of circumstances.
It's assumed that Cibola is very capable of defending itself in the case of an attack, but this has never been tested. The simple fact that even _getting_ to the capitol involves fighting though several hundred miles of jungle then up a mountain range is deterrent enough.
For all the talk of blood and skin and such, the people of Cibola are fairly down to earth. Fisherfolk who have found themselves lifted to prominence, the people of Antukt are resigned to the rules of the empire in a manner familiar to anyone who's ever worked at a branch office. Gold, zealots and most of the scarier drugs come from further inland, and they don't worry themselve too much about it. Their grandfathers grandfathers were brought under the Empire's domain after it was made clear how painful the alternative would be. Comparatively, it's not such a bad gig.
The Empire of Cibola commands many magics. Blood magic, tapestries that shape destiny, drugs that steal dreams, spiders that plant eggs in a mans soul - all of these have been attributed to the Cibolese at one point or another. The reality is a closely held secret, but those in the know do observe on thing - there is no mention of traversing shadow in any of these tales. That lack goes a logn way to explainign Cibola's interests and motives.
Cibola is every worst imagining of Aztec and Inca civilization, combined with jungles that mesh darkest africa with the depths of the Amazon.
Cibola itself serves the role of a low-key villain in the Golden Circle. Not overtly going to war, they still are likely to be in places of interest, pursuing their own agenda and serving as a foil to a PC efforts. Think of them as in a similar role to the Nazi's in Raiders of the Lost Ark, seeking out the secrets of reality and shadow for their own nefarious purposes. There may be occasional political repercussions to this, but they will generally be minimal, as the ruler's of Cibola respect none but Amber, and for Amber they will pay the appropriate price in blood and move on.
Within Cibola, the jungle provide infinite opportunity for adventure. The coast is hundreds, perhaps thousands, of miles long, and Amber was there for years before realizing the Cibolese were also there. Ancient temples, lost civilizations and beasts beyond any kind of recognition are all appropriate to the sort of things you're going to find in the jungles of Cibola.
Player-maintained Wiki: cibola.roadtoamber.com