http://starcraft.wikia.com/wiki/StarCraft_storyline#Pre-Starcraft_History The early zerg wiped out the XelNaga? How come this super race got wiped out by zerg but the terrans and protoss have not after all the fighting? The XelNaga is a fail race.
Well, the Xel'naga at the time were only in one part of space and had no weapons. Or defenses apparently. Which, considering what happened with the protoss, was indeed very stupid. The reason Terran and Protoss survived is timing mostly. When the swarm first attacked, they wanted to find Aiur, and didn't really care for the acquisition of the Terrans. The moment they found aiur they could have taken the whole sector, but the overmind was destroyed within days of that, and the zerg broods started thinning out their own numbers in the brood war. Since that point, they have been building up numbers again, but for some reason they are holding back.
Even better when you consider the Xel'naga lost to what would have been a mostly drone army, as the lore for most of zerg's T1.5 or higher units has them being created after the fall of the Xel,naga. I don't think they even had zerglings either.
They're pacifists. So picture having a well-built house, but no security guards, no gun turrets, nothing. If a mob attacks, and you can't call the police, eventually they'll drive a car through your front window and rush in. Then you hide in the safe room until you dehydrate.
