Battle of Moria

The Battle of Moria (also known as the Battle of Azanulbizar) was a battle that took place in the Dimril Dale in TA 2799 between the Dwarves and the Orcs. It ended in a Dwarvish pyhrric victory.
After the sack of Erebor by Smaug, the refugees led by king Thrór, his son Thráin and grandson Thorin, arrived at Dunland. From there, Thror tried to lead them back to Moria, their first kingdom, only to find it infested with Orcs, led by the Gundabad Orc Azog.
In the battle, Azog swore the wipe out the royal line of Durin. He beheaded king Thror, defeated and captured his son Thrain (taking his Ring) and almost defeated his own son, Thorin. However, the young Dwarf prince picked up an oaken branch to repel Azog's attacks, and using a sword, cut off Azog's arm. The Orc was hauled back through the Dimril Gate and Thorin led the Dwarves, including his companions Balin and Dwalin, to victory.
However, their loses were too heavy to reclaim Moria, and Thrain's fate was unknown to the Dwarves. While Balin and Dwalin mourned the loss of their father, Fundin, Thorin looked through the bodies for his father, to no avail. He deluded himself into believing Azog died of his wounds, but in fact he would return to hunt him during the Quest of Erebor. Thorin also accused the Elves of nearby Lothlorien for looking over and doing nothing to stop the Orcs.