The Core Federation, also referred to as the Unified Core and the Core States, or simply the Federation, was the interstellar federal entity which governed a portion of the galaxy's center-most region of space as the preeminent successor state to the Galactic Empire in the years following the Galactic Civil War.
In the aftermath of the Battle of Endor, the Empire silently slipped into a state of internal conflict in which a bevy of warlords from within Imperial High Command vied for the throne―of all of these warlords, none were as successful as Grand Admiral Rae Sloane, who secured the largest imperial armada and subdued her rivals within a year. In 5 ABY, what was left of the Empire was formally disbanded after the Galactic Concordat's ratification and from its foundations, Supreme Leader Sloane established the Federation as a "reformed, democratically-driven star-nation," according to official Federation statements. Both New Republic officials and independent rights observers, however, often criticized the Core Federation as repressive and worrisome, with a corrupt voting system and heavy restrictions placed on the political rivals of the ruling Federalist Party―there were even rumors of significant military buildup on the Federation's part taking place over a span of decades, a blatant violation of the Galactic Concordat's terms, though the truth of this could never be verified by the Concordat Enforcement Mission.
Despite years of tension, and several well-documented diplomatic crises, relations between the Federation and Republic were largely non-combative toward one another. These star-nations even joined forces during the Galactic Incursion, becoming two of the founding member-states behind the Galactic Coalition in 17 ABY.