Dwarf

Dwarves are a common race on Eberron. The majority of them live in their homeland, the Mror Holds, though many dwarves have migrated all over the continent. They are shorter and stockier than humans, and much longer lived. They aren't native to Khorvaire, but no one knows exactly when they arrived on the continent, or where they cam from. Some of their stories claim that the dwarves came from a land of ice and frost, but the stories don't all agree on this, and a competing narrative is that they are the children of mountains.
While this is enough for the Mror, the origin of the dwarves is hotly debated by scholars. A popular theory is that they originated in the Frostfell, and arrived in Khorvaire via a demiplane in Khyber. If this is true, there could be undiscovered dwarven civilisations waiting to be found in the Frostfell. Another popular theory is that they originated in the Tashana Tundra of Sarlona, and sailed to Khorvaire prior to the human settlers.
Regardless of where the dwarves came from, they arrived in Khorvaire. Dhakaani records, which are more accurate that those maintained by the Mror, show that the Dhakaani encountered the dwarves late in the golden age of the empire, and drove them east until they reached a stalemate. The ancient dwarves couldn't threaten Dhakaan, but they established themselves beneath the Ironroot Mountains and held there. The Dhakaani had no need of the land, and decided it wasn't worth conquering them. 
At some point following this, the exact timing is unclear, a group of dwarves were exiled from their home beneath the Ironroot Mountains, the Realm Below, and settled the mountains above, and the thirteen exile clans were constantly mired in conflict with eachother. When humans came and the Five Nations began to take form, the dwarves were largely left to their feuding. Following the rise of the Kingdom of Galifar, Prince Karrn finally made an effort to pacify the dwarves. The humans took advantage of the dwarves feuding to isolate the clans, and eventually the dwarves were left as lords of their territory, but as subjects of Galifar.
As the dwarves expanded, they discovered ancient abandoned tunnels and outposts, and eventually great subterranean cities. It was clear that these had been built by the dwarves, and it speaks to the Dwarven character that they embraced this is a sign of their shared destiny, rather than pondering what had happened to these cities or why they had been abandoned. During this time, the Last War was underway and Karrnath was imposing heavier and heavier taxes on the dwarves.
Inspired by what they had discovered in Sol Udar, the Realm Below, the Mror convened the Iron Council and declared independence. Whilst Karrnath attempted to retaliate, they didn't really have the resources to seriously press the Mror, and what followed was known as the Age of Gold. The dwarves expanded and explored beneath the earth, and soon learned what had become of the ancient dwarves of the Realm Below.
The ancient dwarves had been wiped out by the Daelkyr, as Sol Udar connected to the demiplane of Dyrrn the Corruptor. First, the dwarves found tools and weapons formed from flesh and bone, and then they found the creatures that created them. Entire colonies were lost and consumed by the aberrations. While the world above fought the Last War, the Mror fought the War Below.
Now, the Mror are locked in a stalemate with the forces of Dyrrn, with neither side meaningfully expanding. Even so, the dwarves are drawing vast wealth from their current holdings and are still in age of prosperity.
There is one dragonmark that manifests on Dwarves, the Mark of Warding, and the associated house is House Kundarak.

Lifespan

350 years