[@ClocktowerEchos]

Kobolds are a stable of Dungeons and Dragons/ Pathfinder as small, humanoid dragonkin that live in tribes (some above ground, but mostly in underground borrows that they dug out themselves). While they view themselves as related to dragons (and the more dragon-like you are, the better! Wings and a breath attack of some elemental nature are positive traits), Kobolds are kind of physically weak individually; That isn't to say that some of them aren't good melee fighters, but they are painfully aware of the fact that if the average kobold warrior goes up against the average warrior of just about any other race in a fair one on one fight it's going to end badly for the kobold. 

What they lack in size and raw physical power, Kobolds make up for with intelligence and cunning partnered with a pragmatic ruthlessness dedicated to keeping themselves alive, but thriving despite the odds. They would arguably be one of the first races on a given planet to figure out how to create explosives and firearms (Making something or a lot of someone's vanish in an explosion is -really- dragon like, and guns go a long way to fighting heavily armored opposition). They are also brilliant trap makers and ambushers, favoring indireact warfare to deal with opposition rather the get bunkered down in a straight up meat grinder battle.

One of the oldest enemies of Kobold kind are the night goblins (Or the goblins that live underground in this setting).  While the two races are similar in many ways, Kobolds don't quite breed as quickly as the goblins do (Granted they are still laid in litters of eggs and grow to maturity in a matter of years, but the goblins have them beat here) so they have to make up the difference in numbers by having better equipment (via better mining and forging abilities), better individual fighters (Goblins being one of the few races that a kobold is on par with, if not stronger then. The fact that Kobolds actually -train- to fight properly is an added bonus) and better team tactics (Kobolds are naturally inclined to work together for survival and the good of the tribe, but they will also train with each other in order to work together as teams and increase their tunnel fighting abilities. Goblins do neither of these things). 

Dwarves are another natural enemy, through to a much lesser extent then the greenskins. In the case of dwarves, the issue is more that they are both underground races that via for the same resources. Other races... well, relations with other races depends on what happens between them.