You may well have to reinstall, Nonsapient, the game itself may be broken.
It happened to me once in 40d16, the game borked and it decided to only make kobold, some animal man, goblin, and elf civs, with kobolds in place of humans and the animal men (I don't remember which kind) replaced the dwarves.
Kobolds sometimes exploded while freezing to death.
pic:
It was pretty hilarious since quite a few other things were broken, but so horribly, horribly broken, dwarf mode would crash on attempting to start.
more on topic, you could murder the dwarven civs during worldgen by making them utterly pathetic, best by making them tiny and weak, and/or setting in their entity file to something like:
[MAX_STARTING_CIV_NUMBER:1]
[START_GROUP_NUMBER:5]
[MAX_POP_NUMBER:50]
[MAX_SITE_POP_NUMBER:25]
and you can remove their [SIEGER] tag so that they will only play defence.
This will make them an utterly delicious target. Then set the other races' values in those fields to maybe 10X their defaults, but maybe not for elves...
Taking away their [DIPLOMAT_BODYGUARDS] and [MERCHANT_BODYGUARDS], and deleting the outpost liaison noble, will look something like the civilization, if it still exists/traders still come, is beaten and in ruins. I wonder what havok will be caused by taking away [COMMON_DOMESTIC_PACK], [COMMON_DOMESTIC_PULL], and [COMMON_DOMESTIC_MOUNT]
You could also make them begin and exist on only normal caves like kobolds.
Note that changing entity definitions after world generation will not modify any existing civs, so don't remove their weapons, armor, or anything that's going to affect you in fortress mode, but editing creature definitions will change creatures at any point in time so long as they already exist.