Orcs: Third Age (p2)

Following the abandonment of Khazad-dûm by the Dwarves, Orcs eventually colonised the abandoned halls, killing King Thrór when he sought to enter his lost realm. This triggered the War of the Dwarves and Orcs, a massive conflict where the Dwarves gathered their full strength and destroyed every Orc stronghold they could find in the Misty Mountains. This and the Battle of Five Armies greatly reduced the numbers of Northern Orcs, weakening their contribution to the War of the Ring.