Before the 14th century, the Ventaxians were highly industrialized, and caused destruction in the planet's ecology through various conflicts. In the year 1367, the Ventaxian leaders began pacifying the planet and cleaning the environment, using the story of Ardra to bring their people together in a common contract. After that, they were a peaceful agrarian society and effectively isolated itself from the rest of the galaxy.
First contact after centuries was made by a Klingon expedition in 2297. Hired Klingon craftsmen went on to construct homes on Ventax II. Sometime after this, a Federation research station was established on the planet to study their culture. In 2367, this station was headed by Dr. Howard Clark.
In 2367, the planet fell into chaos again when, according to the Ardra story, a fabulous thousand-year period of peace and wealth would come to an end and the planet would be turned over to Ardra. A con artist took advantage of this myth and modern technology to present herself as Ardra and to bring the planet under control. She used technology to cause earthquakes, for example. Her true identity was successfully revealed by the crew of the USS Enterprise-D. (TNG: "Devil's Due")
In the episode, many of the details for the precedent-setting case were omitted. According to the script, in the Ventaxian year 931 AA (after Ardra), in the township of Tau Velor, the craftsman Akul K'Ton filed a charge against the home owner Garv Etes. The case was decided in favor of the Ventaxian. 
Syd Dutton discussed the matte painting of the Ventax II surface in the VOY Season 4 DVD special feature "The Art of Alien Worlds". Describing the place as "the Aztec city of the future", he also explained how the shot contained footage of a nearby dam, including its top as the ramp on which people were fleeing. He described the shot as including a temple and cement surfaces.
According to Star Trek: Star Charts (p. 64) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Ventax system was located in the Beta Quadrant. The primary was a G-class star.