The player's character is commanded by Zeratul and Aldaris, two adversaries from StarCraft who have since reconciled their differences to lead their people in the face of the rampaging Zerg.

They are joined by Jim Raynor, a Terran rebel on the run from the Dominion, Artanis, the previous Executor of the third campaign of StarCraft who has recently been promoted, and Raszagal, the matriarch of the dissident dark templar faction in Protoss society.

The second campaign sees the player as a captain in the UED expeditionary force, reporting to the fleet's admiral Gerard DuGalle and his vice-admiral Alexei Stukov.

To secure the sector, the UED plans to overthrow the Terran Dominion and its emperor Arcturus Mengsk, and are assisted in this by Samir Duran, a mysterious psionic ghost espionage agent, and his group of anti-Dominion rebels.

Despite knowing that activating the temple will accomplish Kerrigan's objectives, Zeratul and Artanis proceed with little other choice, wiping the Zerg off Shakuras' surface.

Using the psi disrupter's capabilities, DuGalle and the UED are able to assault the Zerg world Char and take control of the new Overmind growing there.

With the Overmind falling under the United Earth Directorate's command, all operations amongst native factions in the sector are damaged, including Kerrigan's forces.

To begin the campaign against the Directorate forces, Kerrigan and Samir Duran form a reluctant alliance with Jim Raynor, Protoss praetor Fenix, and Arcturus Mengsk to destroy the psi disrupter.

After destroying the psi disrupter, the player leads Kerrigan's forces in a full-scale assault on Korhal, quickly breaking the UED's hold over the planet.

In the aftermath, Kerrigan betrays her allies, destroying a large number of Dominion forces and killing both Fenix as well as Edmund Duke, Mengsk's right-hand man.

Upon leaving Char in search of Artanis, Zeratul stumbles upon a genetics facility run by Duran without Kerrigan's knowledge where a Protoss/Zerg hybrid is being developed.

Before the UED fleet is wiped out, Admiral DuGalle sends a final message back to his family before committing suicide with his pistol.

[15] According to Shane Dabiri, the game's producer, Brood War aimed to drastically increase the significance of the story within gameplay, stating that the team was adding scripting that would allow "Final Fantasy type events" to be played out during the course of a level.

PC Zone praised the inclusion of new units and the balancing tweaks as transforming the original StarCraft "from an okay game into something akin to the mutt's nuts".

[5] GameSpot was also positive in its review, stating that the design of Brood War "contains all the care, detail, and ingenuity of a true sequel" that "completely revitalizes" the original game.

The reviewer praises the "seemingly minor but terribly significant modifications" to the balance of the game, putting the results as "outstanding", but draws concern to the interface's shortfalls in coping with these changes.

GameSpot also notes the music and audio work on Brood War as a bold improvement, describing the voice acting as "completely convincing" in a heavily story-driven single-player campaign that although becoming less innovative in the latter stages, "remains captivating to the end".

The reviewer continued by stating that "while the unit upgrades are good, the scenarios still don't cut it", describing the single-player mission design as an "afterthought" despite the expansion possessing an "interesting" storyline.

Dismissing the multiplayer additions as unimportant, Game Revolution summarized that while "a fun expansion", Brood War was "a mixed bag".

[19] Brood War was a finalist for Computer Games Strategy Plus's 1998 "Add-On of the Year" award, which ultimately went to Age of Empires: The Rise of Rome.

"[24] StarCraft, along with its expansion Brood War, rapidly grew in popularity in South Korea, establishing a successful professional gaming scene.