Helladvergar
They fled at the beginning of the Dark War. Those who didn't -- who still call themselves the Svirfneblin -- are dead or conscripted to fight for the other powers in the Underdark. Theirs is a pitiful lot, mostly as fodder for the front lines, or forced to cast until exhaustion if they have any arcane skills. But they are still recognizably Svirfneblin, even in chains.
The Helladvergar, as they have taken to calling themselves, are not. Their kin would be aghast at what they have become - every taboo of the gnomes, deep or surface, have been either embraced or ignored. They don't embrace life like the gnomes you know -- death is their calling, and they have adapted to it. The worst of them have taken to filing their teeth to sharp points, using them to bite and rip the flesh of their enemies. And their enemies are everyone who is not them.
I believe the war, and what they did to escape, broke them. Those who could not embrace their new attitude couldn't escape in the first place. They had to kill -- not just Drow or Duergar, but each other -- to get away, often with nothing but teeth and nails as weapons. They had to be ruthless in cutting down their enemies, because they were surrounded by those who saw them as nothing more than slaves not yet captured.
Could you have remained sane when surrounded by death and destruction? Could anyone? I don't judge the Helladvergar too harshly, because I understand them. I understand what it is to have enemies at your throat, to be unable to save your friends or family, barely able to save yourself. I know what that does to a person, no matter the species. The Helladvergar have fully embraced what the war did to them, and it is how they will survive. Perhaps one day, after the war is but a memory, they can find their way back to who they were. Or maybe not, and maybe that's better. They have learned a fundamental lesson on life - it's brutal and it's short, and you have to fight for it.
Love me some battle worn Gnomes. Nicely done.