Battle of the Mines of Moria

(1)	The first assault of the Dwarves fails; the defending Orcs force them aside towards the Mirrormere.
(2)	The Dwarves of the Iron Hills enter the battle, fighting their way through the ranks of the Orcs to the steps of the East-gate.
(3)	Dáin, later called Ironfoot, slays Azog at the East-gate, bringing victory for the Dwarves.
(4)	The surviving Orcs flee the field; many of them escape into the south, seeking refuge in the White Mountains.

The battle fought before the East-gate of Moria in III 2799, better known as the Battle of Azanulbizar or the Battle of Nanduhirion. This was the culmination of the nine-year War of the Dwarves and the Orcs, in which the forces of Thráin II of Durin's Folk attacked Azog the Goblin in his lair of Moria. The resulting battle was fierce and horrific; dreadful numbers were slain on both sides, and many of Azog's Orcs fled away into the south, to make trouble for the world in later years.

It should be said that the identity of this battle is not established beyond doubt. The battle is mentioned in passing in The Hobbit, but all we're told is that in the aftermath 'the Goblins had spread in secret' (The Hobbit 4, Over Hill and Under Hill), which seems to be a reference to Azog's routed forces escaping the valley of Nanduhirion. The only real alternative would be for the 'Battle of the Mines of Moria' to refer to the battle of the Dwarves of Khazad-dûm against the newly-awakened Balrog, long before Azanulbizar, but for various reasons that seems a less likely possibility (for instance, after that battle the Goblins did not 'spread', but instead gathered together in Moria).