The term Imperial Core was adopted by the New Republic to refer to the vestiges of the Galactic Empire that remained active within the Core region during the latter portion of the Galactic Civil War. While the New Republic spoke of the Imperial Core as a singular entity, it in reality consisted of varied Imperial factions that underwent significant changes over time, encompassing both loyalists and perpetually warring warlords.
Initially, "Imperial Core" described the highly imperialized Core region during the height of the Imperial Period. Thus, it encompassed all star systems within the Core.
Following the death of Emperor Palpatine at the Battle of Endor in 4 ABY, the Galactic Empire began its decline. However, the Empire still maintained a strong presence within the Core between 4 ABY and 6 ABY. The Core Worlds and Colonies remained loyal to the Imperial Ruling Council, while the Deep Core became a haven for Imperial warlords who carved out their own petty empires. Prominent examples include Lord High Admiral Blitzer Harrsk's Zero Command and Superior General Sander Delvardus' Eriadu Authority. In 6 ABY, the New Republic initiated its campaign to seize control of the Core. After the liberation of the galactic capital of Coruscant in 7 ABY, the New Republic supplanted the Empire as the primary galactic power. The Core Worlds and Colonies largely aligned with the New Republic, although some refused.
In subsequent years, the collection of Deep Core warlords and remaining Imperial loyalists within the Core came to be collectively known as the Imperial Core. Their military force was even referred to as the Imperial Core Navy. Despite this, the Imperial Core's forces remained fragmented, especially among the Deep Core warlords who were engaged in constant infighting. Imperial loyalists were frustrated by the warlords' squandering of resources on internal conflicts rather than targeting the New Republic.
In 8 ABY, the New Republic captured two major Imperial planets in the Core Worlds: Anaxes and Kuat. By 9 ABY, remaining Imperial systems in the Core Worlds and Colonies included Carida, Rendili, Chasin and Kelada systems. Meanwhile, the warlords' holdings in the Deep Core encompassed, among others, Lord High Admiral Harrsk's Zero Command, Superior General Delvardus' Eriadu Authority, High Admiral Teradoc's Federated Teradoc Union, and Moff Brill's Constitutional Protectorate of Prakith.
In 10 ABY, the reborn Emperor Palpatine unified the Imperial Core, including the Deep Core warlords, with other Imperial elements throughout the galaxy. This Imperial Coalition drove the New Republic out of the Core and reconquered Coruscant, but the alliance proved short-lived, collapsing into a widespread Imperial Civil War. Following the defeat of the reborn Emperor Palpatine, the New Republic regained control of the Core, and the warlords retreated back to the Deep Core. Carida remained a significant Imperial loyalist world within the Imperial Core until its destruction in 11 ABY.
In 12 ABY, Imperial Admiral Natasi Daala assassinated thirteen Imperial warlords, including powerful Deep Core figures like Harrsk, Delvardus, Teradoc, and Yzu, during a conference at Tsoss Beacon. Daala thus reunified the warlords' forces into a single fleet. After Daala's defeat during a brief and unsuccessful campaign against the New Republic, Admiral Pellaeon assumed command of the United Warlord Fleets and merged them with Imperial loyalist systems in the Rim, forming the Imperial Remnant. Furthermore, Pellaeon salvaged any useful materials and vessels from the assassinated warlords' former holdings in the Deep Core, relocating them to Imperial Remnant space.
Daala and Pellaeon's actions significantly diminished the Imperial presence in the Imperial Core. The few remaining Imperial warlords in the Deep Core, including Moffs Foga Brill and Jmanuel Tethys, became known as the replacement warlords. While still commanding considerable military strength, these warlords were far less powerful than the thirteen executed by Admiral Daala. In the following years, the Imperial Core's primary objective was to prevent further territorial losses. The Deep Core was heavily fortified, with numerous starships patrolling the border between the Imperial Core and the New Republic, including IPV-1 System Patrol Crafts, TIE/rc starfighters, Interdictor-class heavy cruisers, Strike-class medium cruisers, Adz-class patrol destroyers, and Imperial Patrol Frigates. Following the end of the Black Fleet Crisis in 17 ABY, surviving Imperial forces from Black Sword Command escaped the Koornacht Cluster and joined the Imperial Remnant and other Imperial forces. Approximately 60 warships, equivalent to ten superiority fleets, including Interdictor-class heavy cruisers, Victory-class Star Destroyers, Imperial-class Star Destroyers, and the Super Star Destroyer Intimidator joined the Imperial Core Navy. Four Victory-class Star Destroyers bolstered the Deep Core warlords.
In 17 ABY, Admiral Daala consolidated the Deep Core warlords under her leadership. The replacement warlords and the Council of Moffs of the Imperial Remnant then agreed to launch a joint campaign against the New Republic. This campaign proved disastrous, leading the Imperial Remnant to negotiate a peace treaty with the New Republic two years later. However, the remaining replacement warlords rejected these agreements.
These Deep Core warlords subsequently established the Second Imperium. They pooled their resources to create the Shadow Academy, a training facility for Dark Jedi. The Second Imperium was eventually defeated by the New Republic and the New Jedi Order in 23 ABY. In 25 ABY, the New Republic launched a successful campaign to eliminate the remnants of the Second Imperium and the various Imperial warlords who had refused to accept the peace treaty between the Imperial Remnant and the New Republic. By the time of the Yuuzhan Vong War, all traces of the Imperial Core had finally been eradicated from the Deep Core.