We all know that the Great Dwarven Empire disappeared around the year 1400 A.D. Even though it is recent compared to ancient civilizations such as the Maya, it is very difficult to pinpoint an exact date due to the hidden locations of their dwellings, and almost all of them have suffered from numerous cave-ins or are submerged in magma.
Theoretically after eradicating their elven rivals and the surrender of the Goblin Empire to the Humans around 1150 A.D., they should have been free to develop new technologies in peace with little interference.
Some scholars suggest that earthquakes and movement of tectonic plates caused massive cave-ins and magma flow, which resulted in what we find today.
Others reject this theory and claim that civil war broke out between the Great Dwarven Empire, and a new schism. These two groups sent ambush parties to destroy vital components of each fort. Each party was successful, and there were too few dwarves remaining to recover.
However, some more radical historians suggest that it was simply the dwarven nature that led to their demise. Egyptian hieroglyphs show dwarves creating an above-ground megafortress made entirely of cesium, before redirecting the Nile river into its center. Events such as these had created catastrophic losses of population. Roman traders documented that after the untimely death of a domestic animal, dwarves would often burst into a violent rage. These mood swings were said to be infectious, and the Romans were forced out of the mountains dodging large furniture.
One new theory is that the Dwarves had dug into the sea-floor and created a large flood.
Any other theories?