The Great Dwarven Union rules over all dwarves, whether they like it or not.
The Great Dwarven Union traces his history back to the Hadean dwarves of Jura City. Emperor Thule wanted highways built by dwarves, but his young empire had little money. The Hadean dwarves were quick to take advantage of this: Thule ceded all authority over all dwarves to Jura City. This caused much outrage among other dwarves, especially Malachite dwarves. However, Thule was firm and kept his part of the bargain.
In response, many dwarves refused this authority, but many other dwarves embraced it. Soon the Hadean dwarves found the strangest assortment of dwarves moving to Jura City to live in the new capital. They were nothing like Hadeans. Some lived in the badlands, wore bone armor, and hunted wild animals. Others were farmers, more like elves than dwarves. Having enough of these claiming to be proper dwarves, the Chairman of Jura City went back to the Emperor to complain about these unwanted dwarves. The Emperor had no mercy. The Great Dwarven Union got all dwarves.
When the Empires split, Jura City went with the Griffin Empire. Even so, the Great Dwarven Union sought to remain neutral. Their authority still extended over all dwarves in all places, across empires. This often resulted in the absurd situation where the Empires were at peace, but the dwarves were at war. The Great Dwarven Union slowly forced dwarves to join the Union. Meanwhile, other dwarves sought to break away.
In modern times, Jura City has been a stable oasis in a desert of woe. Refugees from the collapsed Griffin Empire settled outside of Jura City, rapidly swelling her size and turning her into a country. Meanwhile, as the Malachite dwarves rebelled against the Unionion, rebelled against the Dragon Empire, then used the power of an empire to counter the power of the Great Dwarven Union.
At this point, the Great Dwarven Union is a Union in name only.
Here are some adventure hooks for the Great Dwarven Union.