Did the original StarCraft come out so long ago that you can't remember what happened in the game, perhaps because you weren't alive then? Or do you just need a refresher? Here's how to catch up on the lore... fast.
The Terrans hate the Zerg. The Zerg hate the Protoss. The Protoss hate the Terrans. But sometimes the Terrans and Protoss team up. Sometimes the Terrans use the Zerg for their purposes.
It all began in the year 2499, and if you want fully annotated lore history, the StarCraft Wiki's StarCraft Storyline will break it down. That should be your first stop.
In the original StarCraft, each of the three races has its own storyline campaign. The short-short version of the Terran campaign is this: Jim Raynor, a man at odds with the Conferdate-flag waving human government of the Koprulu Sector. By game's end, Raynor has teamed up and then been betrayed by the anti-Confederate Sons of Korhal, who assert themselves as the Terran Dominion under the leadership of Arcturus Mengsk. Raynor breaks away to form a group called Raynor's Raiders.
Watch some StarCraft Terran campaign cinematics to soak this in:
The hive-mind Zerg, a race created by the mysterious and now-absent Xel'naga, spend their original StarCraft campaign battling Terrans, kidnapping possible Raynor love interest Sarah Kerrigan, turning her into a half-human/half-Zerg hybrid, and trying to find, then assaulting the homeworld of the Protoss.
Here are the Zerg cinematics from the first game to flesh that out:
The third StarCraft I campaign involves dissension among the other race founded by the Xel'naga, the spiritual warrior Protoss. Tassadar, who teams with Raynor in a fight against the Zerg, is summoned back to his homeworld, attempts overthrow of the ruling authorities but then resigns himself to helping the Protoss powers-that-be defeat the Zerg Overmind. Tassadar martyrs himself in the process.
Watch the Protoss cinematics from StarCraft I for more on this:
The StarCraft Brood War game mixed things up, pitting incoming forces from distant Earth against all of our lead races and leaving Mengsk's Terran Dominion in a rebuilding process, the Protoss without their matriarch, the Zerg-manipulated Raszagal, Raynor still with his Raiders and Kerrigan - the Queen of Blades - in charge of the Zerg.
And that brings us to StarCraft II: Wings of Liberty, the Terran-focused sequel. (The other two races will each be featured in the campaigns of their own StarCraft II games, to be released who-knows-when.)
With Kerrigan in power, the Protoss shaken and signs of a Xel'naga return, what's next? Here is how Blizzard sets up the Terran situation:
Mengsk and his forces have regrouped on Korhal IV. His first order of business was to rebuild the Terran Dominion. In Kerrigan he had found a new target for revenge, and he'd always been happier with a goal to work toward anyway. The Dominion has since become the most powerful force among the terran factions, having taken over many of the original Confederate worlds.
The Kel-Morian Combine and the Umojan Protectorate have been preparing for the inevitable war with either the zerg or Mengsk. The UED task force was almost completely destroyed in Brood War; only a few isolated pockets of survivors remain hidden in the Koprulu sector.
Jim Raynor has led a resistance movement against the Dominion, but that has been a losing battle. Arcturus Mengsk has used his greatest weapons—the media and propaganda—to marginalize Jim's efforts. Raynor seems to be losing faith, drinking heavily and haunted by the ghosts of his past. He has never forgiven himself for letting Kerrigan be taken by the zerg.
The official Blizzard history of StarCraft, their Story So Far from which the above section is excerpted is another must-read.
Finish your StarCraft II storyline cramming with our sister site io9's refresher on StarCraft lore, which puts the fiction in the context of some of the sci-fi genre's other greats.