The Sagittarius Frontier is the colloquial name given to the eastern regions of the Sagittarius galaxy during the League Era. The Spinward and Hail regions are considered part of the Frontier, as well as substantial parts of the Midnight Edge and Cawdren Heath regions.

As human civilisation spread outwards from Sol, it naturally became more thinly-spread with distance, and central government became more tenuous. Systems on the far side of the galaxy tended to be more independent and less regulated.

Under the Galactic Defense League, these distant systems became havens for people dissatisfied with the League, and particularly for people who the League was dissatisfied with. The GDL's military lacked the resources to patrol the Frontier as heavily as the more populous regions to the west, and its oversight had many blind spots.

After the War of 4404, the Frontier was slowly brought under the jurisdiction of the new Core Governance. Systems that had been neglected by the League were given more attention and the resources they needed. Eventually, the regions that had been part of the Sagittarius Frontier were no more lawless than any other part of the Governance.