The Core Worlds are a group of planets within the Koprulu sector.
The core worlds were originally thirteen planets ruled over by the Terran Confederacy. Their architecture was rather uniform. An increasingly hectic urban lifestyle was predominant on most of them.
Unlike the fringe worlds, the core worlds were not characterized by location, but simply by their importance. (e.g. Mar Sara was both a fringe world and core world). Under the Confederacy, the Core Worlds often relied on exports to remain viable. By the time of the Confederacy's fall however, nine of these worlds had been laid waste to by the zerg.
Under the rule of the Terran Dominion, the term "core worlds" is still in use. With the zerg invasion that began the Second Great War, Emperor Arcturus Mengsk pulled the Dominion Fleet back to protect these worlds. They were fortified and the First and Second Fleets combined to protect them. Conscription stations opened across them after the defeat of the Kel-Morian Combine.
Refugees from the fringe came to be turned away from core world systems.
- Brontes (invaded by the zerg)
- Char (invaded)
- Chau Sara (also viewed as a fringe world, invaded, purified and later became a Kel-Morian Combine world; was the subject of a Dominion vs zerg battle during the Second Great War)
- Dylar IV (invaded)
- Korhal IV (decimated through nuclear bombardment)
- Mar Sara (also viewed as a fringe world, invaded and then purified)
- Tarsonis (capital world, invaded)
- Tyrador IX (survived)
- Dylar IV
- Korhal IV (capital world)
- Nephor II
- Tarsonis (largely depopulated and independent; Dominion and zerg presence)
- Tyrador IX
According to the manual of the original game and Overmind, the Confederacy consisted of "nearly a dozen" and "thirteen worlds" as a whole respectively. With the revealing of numerous other Confederate colonies, it appears that this number refers to the worlds of Confederecy itself, i.e. Core Worlds, since there were distinctions made in the original StarCraft between fringe colonies and main planets.