As of 2154, the Andorian Empire employed listening posts to guard its borders. Regulus was the closest accessible star known to be outside the maximum range of those listening posts. (ENT: "Kir'Shara")
In the Star Trek: Typhon Pact novel Paths of Disharmony, the Andorian government formally secedes from the Federation in 2382 following the controversy over revelations made by the Tholians that the Federation classified records roughly a century prior that the Andorians would come to believe possibly held a key to aiding them in a reproductive crisis brought on by the need for four genders to procreate. The crisis had been exacerbated by the Federation's war with the Borg, and the subsequent damage to Andor, that was the focus of the Star Trek: Destiny trilogy.