During the 22nd century, the Valakians suffered from a plague that was killing off its entire population. In 2149, the plague was responsible for causing 12 million deaths on Valakis, causing the Valakians to dispatch numerous spacecraft to seek help from offworlders.
The Enterprise offered to aid in search for a cure and while they were visiting the planet, the ship's doctor, Phlox, discovered that the epidemic wasn't being caused by a virus or bacteria. Instead, the illness was genetic; the proteins that bind to Valakian chromosomes were deteriorating. This had been going on for thousands of years but the rate of mutation had accelerated over the last few generations. Based on his projections, Phlox predicted that the Valakians would be extinct by the 24th century.
Furthermore, Phlox discovered that the Menk had the potential to become the dominant species on the planet. The Enterprise crew realized they could not interfere with the natural evolution of the two species on Valakis but agreed to offer drugs that would ease the symptoms of the disease. Because he thought the Valakians could not deal with warp technology on their own yet, Enterprise Captain Jonathan Archer declined to give warp technology to the Valakians for the purpose of finding a cure. (ENT: "Dear Doctor")