The Scutum-Centaurus Arm is a region of the Milky Way that has been protected by the True Divine for thousands of years. It is bordered by Partizan, and thus by most of the Stels of the Divine Principality. To the Principality, it is Caelestia Nullius or "no man's sky".
In the first half of the Perfect Millennium, the Tranquil Princept had an encounter with the True Divine, and pledged the Principality would not enter the Scutum-Centaurus arm until the empire dissolved into an equitable society. This was the origin of the Curtain of Divinity.
After Dahlia's ascension to the throne, the Pact of Necessary Venture was formed; their initial plan was to invade the Scutum-Centaurus arm, use its resources to build a fleet, and take over the Principality. Initial attempts were met with extreme force by Autonomy Itself.