Through a Glass, Darkly
The events surrounding how Vulcan officially became a part of the empire following first contact with Humans in 2063 have been lost to time. Some say the Vulcans joined the empire believing they could manipulate Humans from behind the scenes, while still others suggested that the Vulcans joined feeling a sense of weakness and a need for self-preservation. Having fought a devastating war against the Romulan Star Empire between 1939 and 2041, it could be the latter case which prompted Vulcans to offer themselves as vassals of the empire, rather than full partners. Whatever the case, Vulcan and its people would play a key role in helping to expand the borders of the Terran Empire.
T'Pau, who had been a minor diplomatic official at the time of first contact, would eventually become Vulcan's head of state. It was through her actions and her ability to manipulate one Emperor after another that allowed Vulcan to be both a vassal world within the empire and yet maintain some of its autonomy. Initially T'Pau lured emperors into her bedchamber through her own charms, but then later used a cadre of seductresses in the Imperial Palace to sway and influence the empire's officials. Her agents were equally adept at wielding psionic powers and had access to a huge collection of ancient Vulcan poisons which alluded medical detection.
During the glory days of the Terran Empire, T'Pau, the reclusive mistress of Vulcan lived in a citadel on the Plain of Tai-La. Its roofs had gleaming liquid ludugial gold held into place by force fields. There were also musk-scented corridors, secret passageways, spy holes, a treasury and a torture chamber. Throughout the huge complex walked servants, many of whom had had their eyes or tongues cut out. Those who were blind moved about through clairvoyance.
With the rise of the Klingon-Cardassian Alliance, Vulcan, like Earth, was subjected to a planetary bombardment. What little surface water the planet had boiled away under the heat of Klingon disruptors. After coming under Alliance control, Vulcan became a prison planet where members of the Terran Rebellion, dissidents, and pirates were sent to allow its desolate surface conditions to determine the fate of the prisoner. Those who were sent to Vulcan sometimes fought to the death for what little water could be found in the planet's few remaining cities. The unrelenting thirst caused by Vulcan's desolate conditions drove some prisoners to drink the blood of those they had killed.
Despite the conditions on the surface, the Vulcans never abandoned their homeworld. What's more, they continued to run most of criminal gangs who dominated the planet's population. Alliance officials chose not to bother with any form of warden station and simply monitored the planet from orbit to ensure those sent to Vulcan never left. (Through a Glass, Darkly)
The Glass Empires Universe
Although initially becoming a slave world of the Terran Empire following first contact with Humans in 2063, the fortunes of Vulcan would change radically in the 2150s as a rebellion had broken out against the empire. When the Empress Hoshi Sato was taken prisoner by the rebels while en route to Deneva, she enlisted the help of her former shipmate, T'Pol, in gaining her freedom. Although T'Pol had joined in the rebellion against the empire, she switched sides after uncovering a plot to murder her by fellow rebel T'Pau. T'Pol would eventually kill T'Pau. For her assistance to the Empress, T'Pol was named the Supreme Regent of Vulcan. Moreover, Vulcans and their world were elevated to a status equal to that of Humans and Earth within the empire. (ENT novel: Age of the Empress)
Following Spock's rise to power as the emperor of the Terran Empire, Vulcan played a vital role in his plans for the survival of the empire's people. In 2280s and 2290s, using both Captain Saavik and the Vulcan mind-meld, Spock created a number of sleeper agents throughout the planet's population who not only saw the empire as doomed, but whose main purpose was to bring about the fall of the Klingon-Cardassian Alliance once it came to conquer and dominate Vulcan and Earth.
Events on Vulcan during the latter days of the empire did not go unnoticed by the empire's neighbors. Using spies and infiltrators, the Romulans became aware of what appeared to be a growing pacifist movement on the planet. As far as the Romulans could tell, the movement was not a government sponsored initiative, but was grass-roots in nature with members seeking out their family and friends.
With the rise of the Klingon-Cardassian Alliance, ships came to Vulcan and exported large portions of its population to serve as slaves. Those exported included Saavik and the sleep agents. (The Sorrows of Empire and The Mirror-Scaled Serpent).