(written from a Production point of view)
The Triangle Campaign guidebook was a sourcebook for FASA's Star Trek: The Role Playing Game. It described an area in space where the Klingon, Romulan, and Federation territories merged to form a triangle of independent space. The area was a haven for renegades, pirates, entrepreneurs, and rascals of all types.
The guidebook also describes several independent governments within the area. The Baker's Dozen was a group of thirteen planets that were founded by a Starfleet officer that was forced to abandon his ship during the later stages of the Earth-Romulan War. The IKS was a group of independent Klingon worlds which were a haven for renegades that had tried to take over the Klingon Empire.
The OMCA was a small group which was an offshoot of the main Orion colonies. The Mantiev colonies were a group of four planets banded together into a mining consortium. The consortium splintered and a civil war ensued. The Romulans provided weapons and equipment to one side while the Klingons supported the other. It was used as a testbed by both governments for their newest equipment.
The major governments had an uneasy détente, as none were strong enough to gain the advantage. The areas were considered outside the normal treaty areas between the governments. The Romulans were probably the weakest of the three in the region as they had the least ships. They were able to fool the other governments into thinking they were the strongest because they would rotate new starships to the area, make sure they were seen, and then send the ships off to where they were needed within the empire. The Klingons had the most ships, but most were older designs which would have been outclassed in battle. The Federation were in the middle as far as numbers of ships compared to the Klingons and Romulans, but their technological superiority gave them the edge, even though they were unaware of that edge.
The Federation maintained Starbase 10 and two outposts in the area. There were also independent planets not aligned to any of the major powers or the independent governments. One of the most interesting planets in the Triangle was Marram IX. The planet contained a group of scientists that were captured by Klingons when they came into the area. The planetary governor was the legendary Koloth.