Military action
Dwarven culture erupts into civil war. The Hammerbearer is slain, brother turns against brother, and a people driven from their homeland.
Of the three generals supporting the Hammerbearer, Loghain ??? slowly became more aggressively militaristic until the rift erupts into war. An assassination of their king damaged the loyalties of many of the people, causing massive divides to either side of the war. This dragged on for 5 years before Logain and his followers were beaten back into a corner and retreated deep underground. Declared exiles and struck from their histories, a weakened dwarven empire started to repair deep wounds.