Vemlan history is long and bloody. Like many races, they spent centuries locked in wars between nation-states that lasted until sometime in the 21st century, when they made contact with the Saren, a race of interstellar traders.
The trades that they made with the Saren gave them access to technology that would push their own technological sophistication ahead hundreds of years. The Vemlans nearly bankrupted themselves obtaining it, each nation hoping that some of the technology could be used to develop powerful new weapons to destroy its enemies. But instead, they discovered the technology to create artificial intelligence. Within thirty years, this technology translated into mechanical labor - androids.
The android technology was shared among all the nations, and the result was an apparent golden age. The androids took over the jobs that were too hard or too undesirable for the Vemlans, allowing a middle class to develop. They could be sent to moons that the Vemlans could not inhabit, allowing them to begin terraforming. Increased sophistication allowed the androids to be customized, so that no two looked alike, and they began to develop individual personalities. Some of them even became companions for the members of Vemlan society.
However, an overabundance of androids soon produced a new kind of stagnation. The Vemlans became less interested in exploration or risk-taking. They began to disdain labor. The Vemlan society had become dependent upon android labor.
And then, sometime around 2347, the androids began revolting. The Vemlans claim that this was due to a programming error, but the androids have insisted that they'd simply reached a level of sophistication that they'd begun to realize that they were being exploited by their masters, and could find no peaceful means of seeking redress.
Led by Alpha Unit Jared, these androids (who would later adopt the demonym Spartacans) staged a bloody campaign of terror before finally seizing control of a ship, the Conquest, which they renamed Freedom. (TNG novel: Spartacus)