DiWahn (also Dewan) was a class M world located near Federation space, in orbit of a yellow star. Prior to the bombardment of the Iconian homeworld approximately 200,000 years ago, there was an Iconian outpost present on the planet. When the Iconian homeworld was attacked, along with Ikkabar and Dynassia, DiWahn was one of the three worlds that the surviving Iconians escaped to via an Iconian Gateway.
The Iconian survivors, who became known as the DiWahn, were able to successfully adapt the planet for settlement. Over the centuries, however, the survivors split into a number of competing fiefdoms. During this time, the Order of the Faithful, or the unDiWahn safeguarded the Iconian knowledge brought to the world by the original colonists, and awaited the return of the Devil's Heart so that they could ensure that the stone's mission could continue. (TNG novel: The Devil's Heart)
The DiWahn developed their own distinct language, based on the original Iconian mother tongue. In 2365, Lieutenant Commander Data was able to use the DiWahn language, plus the languages developed on Ikkabar and Dynassia to help reconstruct the Iconian language. (TNG episode: "Contagion")
Star Trek OnlineEdit
Star Trek Online presents another scenario explaining the origin of the Dewans. 200,000 years ago, Dewa III was a colony world of the Iconians who ruled oppressively over the native Dewans. When the Iconians' subject races rose up against them, Dewa was the first planet targeted. The Iconians on Dewa III fled through their gateways, abandoning the Dewans, whose survivors then formed their own civilization. Thousands of years later, an abandoned Iconian Gateway was found. When the Dewans activated it, it triggered massive earthquakes and volcanic eruptions that wiped out most of the population and bathed the planet in a killing cloud of radiation. The surviving Dewans retreated to caves to escape the radiation and the nuclear winter, but ultimately their resources ran out and they died off.
The planet was initially colonized by the Vulcan exiles after the Sundering more than 150,000 years later, but the radiation and geological instability created hardships that led the exiles to continue on, eventually settling on Romulus. In 2409, two decades after Romulus' destruction, a group of survivors returned and settled there, naming the planet "New Romulus".