The border between Vulcanian space (left) and the Andorian Empire in 2154.
Vulcan(ian) space was the territorial region of space claimed by the Vulcan High Command that surrounded the Vulcan system.
According to T'Pol, Paan Mokar's sole value to the Andorians was its strategic location near Vulcan space. (ENT: "Cease Fire")
In 2153, Jonathan Archer reasoned that if Enterprise NX-01 could get to Vulcan space before Klingon attackers repaired their engines, they'd "think twice about giving us any more trouble". (ENT: "The Expanse")
The star Regulus was located adjacent to both Vulcan and Andorian space, just beyond the range of Andorian listening stations. During a planned attack on Andoria, V'Las assembled a fleet of Vulcan starships there during a planned invasion in 2155. (ENT: "Kir'Shara")
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