From the current development logs, it appears that kobolds are consistently slaughtered during world-gen. I had a couple ideas that might help.
First, you could have kobold civilizations randomly, spontaneously arise in otherwise unsettled parts of the world at varying times. This might be capped by a maximum number of kobold civilizations for the entire world, but it would allow new threats to appear and harass the other races. Kobolds should also grow their numbers by the value of goods stolen, rather than conquest of other territory.
Second, you could have kobold civilizations be migratory, so that instead of fighting invaders, they have a good chance to move to a safer spot. If they did sneak away in the night, this would cancel any wars previously declared against them.
Third, you could give civilizations or settlements a stealth rating. In order for a race to launch an attack against another civilization or settlement, it would first have to overcome the stealth rating. They could periodically re-check to be able to attack, but stealth ratings for kobolds could also increase based on their power level. This could lead to situations where the dwarves declare war on the nearby kobold civilization, quickly destroy one nearby kobold site, but then spend the next 200 years searching for the last annoying group of kobolds. All the while, the remaining kobolds are still harassing and stealing from the dwarves, growing more powerful. It would be good if a civilization had to actually commit its warriors to a search for the kobolds. This way, if they sent 200 dwarves to look for the kobolds in year 586, those dwarves wouldn't be available to launch an assault on the nearby goblins, but they may come back after a year without having found anything.