The Galactic Republic "Core" along with the Rim around the time of 22,000 BBY The term "Rim" was a somewhat disparaging, informal way of referring to the outermost regions of the galaxy. Specifically, it encompassed the Expansion Region, the Mid Rim, and the Outer Rim Territories. This concept of the Rim was frequently contrasted with the Greater Core, often simply called the Core, which was another informal designation for the galaxy's innermost regions. The Core included the Core Worlds, the Colonies, and the Inner Rim. Despite never being officially defined, the distinction between the Core and the Rim carried significant cultural and political weight throughout the galaxy's history.
The differentiation between the Core and the Rim began in the earliest days of the Galactic Republic. At that time, the Republic's territory was roughly equivalent to the Greater Core, while the rest of the galaxy was already known as the Rim. Consequently, those living in the Core often viewed themselves as superior and more civilized compared to the Rimmers. During the Expansionist Era, the initial version of the Rim was essentially the same as the modern Inner Rim, which was later absorbed into the Greater Core. Large-scale colonization of the Rim commenced during the Great Manifest Period. The contrast between the secure Core and the perilous Rim, which was dominated by the Hutts and the Tionese, motivated many Rim worlds to join the Republic, thereby accelerating its expansion across the galaxy.
Many millennia afterwards, during the Pius Dea Crusades (around 11,000 BBY), the Rim suffered greatly at the hands of the Republic, which was then controlled by the Pius Dea sect. Even after the crusades ended, the tensions between the Core and the Rim lingered throughout the galaxy's history. Moreover, the Rim was often neglected by the various galactic governments. When the Mandalorian Wars began, the Mandalorian Neo-Crusaders attacked the Rim without prompting any response from the Republic. During the New Sith Wars, the Republic lost control of the Rim to the Sith and separatist factions. At that point, the galactic government was unable to even maintain the HoloNet communication network with the Rim.
In 1000 BBY, after the New Sith Wars concluded, the Ruusan Reformation led to the disbanding of the Republic Armed Forces in favor of developing local sector forces. This reform was less popular in the Rim because the poorer, more remote sectors of the Rim were unable to replace Republic forces on their own. In the Republic's final centuries, its authority in the Rim gradually declined. In 124 BBY, the Republic designated the entire Outer Rim Territories and portions of the Mid Rim as a free-trade zone with the goal of stimulating the economy and strengthening ties between the Rim and the Core. However, this project failed for a variety of reasons. Later, the taxation of trade routes in the Rim fueled separatist sentiments. In the Republic's last decades, vast areas of the Rim were either abandoned to the Hutts or exploited by corrupt senators. At that time, the Galactic Senate was divided between the Human-dominated Core Faction and the Rim Faction, which supported non-Human interests. During the Clone Wars, the Fourth Constitutional Amendment granted more voting power to planets in the Core Worlds, Colonies, and Inner Rim, which led Rim worlds to secede and join the Confederacy of Independent Systems. As the Clone Wars drew to a close, the Separatists strengthened their positions within the Rim territories. After the war, the newly established Galactic Empire faced challenges in its efforts to reconquer the Separatist holdouts that were strongly entrenched in the Rim. During the Imperial Period, the Empire outlawed slavery within the Rim. During the Galactic Civil War, the Alliance to Restore the Republic received more support in the Rim compared to the Core. Immediately following the Battle of Endor, numerous worlds joined the New Republic, with the majority of these worlds being located in the Rim territories.
Decades later, during the Yuuzhan Vong War, the New Republic defense forces were criticized for abandoning the Rim to the Yuuzhan Vong.