Defense of Gnomeregan

The defense of Gnomeregan was one of the longest military actions of the Second War, starting before or concurrent with the Horde's invasion of Lordaeron and lasting through their retreat to Blackrock Spire.

Background
Immediately prior to the Second War, Orgrim Doomhammer rallied the Horde to begin expanding from conquered Stormwind. The first phase of his plan was an attack on Khaz Modan, aimed at gaining access to metals and fuel that could be used for building a fleet of ships. In response the dwarves had demolition teams collapse mountain tunnels leading into the region and called upon their gnomish allies for assistance. The two races pooled their resources to establish defensive positions across Khaz Modan. Despite this, the defenders of Khaz Modan couldn't stop the orcish army. The orcs swept through Khaz Modan, crushing a number of dwarven and gnomish small settlements, outposts, and armories before the Horde's onslaught. He then constructed a fleet of transports, using it to sail most of his warriors to the southern coast of Lordaeron and begin a campaign against the humans. Kilrogg Deadeye and his Bleeding Hollow clan were left behind to complete the conquest of Khaz Modan and consolidate the orcs' control over the Ironforge mountains.

While the dwarves were seen as a bigger threat, Gnomeregan itself would come under assault from the Horde.

Defending Gnomeregan
In order to defend Gnomeregan, the gnomes had rigged explosives throughout the forest and hills that surrounded their capital. As such when the Horde sought to destroy Gnomeregan, many of the orcs would fall into booby traps before they even reached the gnomish capital. To further defend their home the gnomes had created an impenetrable iron gate, which successfully survived weeks of bombardment from Horde siege engines. Faced with no success in cracking Gnomeregan open Doomhammer would call off and order the Bleeding Hollow to keep the gnomes confined within their city, as they were doing with the dwarves in nearby Ironforge.

The Bleeding Hollow continued to keep the gnomes confined, batter the gates of Ironforge and the rocks around it for months, as the rest of the Horde fought against the Alliance across continental Lordaeron. Doomhammer eventually withdrew from his own siege against Capital City and retreated to Khaz Modan, hoping to regroup with Kilrogg's forces before marching north again. The warchief assumed that Khaz Modan had long been conquered, and he was surprised to learn that this was not the case.

Kilrogg advised Doomhammer that it would be imprudent to abandon the siege now, as it was keeping the Bronzebeard nation contained. If the dwarves were allowed to leave Ironforge, Kilrogg argued, they would fall upon the Horde and force it to fight two armies instead of just one. Doomhammer conceded, ordering Kilrogg to keep as many warriors as he needed to hold the dwarves in Ironforge and harry the approaching humans, while the rest joined the bulk of the Horde in their march to Blackrock Spire. He hoped that Kilrogg would later be able to complete the siege and attack the Alliance from behind as they pursued the Horde.

The Alliance did not pass Ironforge by, however. On the recommendation of Turalyon, the Supreme Commander Anduin Lothar led an assault against the Bleeding Hollow orcs and caught them off guard, as they were still focused on attacking the city gates. An entire row of orcs was mowed down before they could turn to face the Alliance. As the Alliance pressed their attack, Ironforge's heavy doors opened with a supporting attack from the besieged dwarves. The two armies quickly cut down the orcs between them. Gnomeregan was liberated and both the dwarves and gnomes pledged their support to the Alliance.

Legacy
The role of the Alliance in liberating Gnomeregan and Khaz Modan during the Second War strengthened relations between gnomes and humans and thus when the Alliance began to splinter some years later, the gnomes of Gnomeregan led at that time by Gelbin Mekkatorque remained with the Alliance.

The Bleeding Hollow being forced to watch over both Ironforge and Gnomeregan essentially kept them away from most of the Second War's campaigns. This may have contributed to them remaining a viable fighting force during the Invasion of Draenor.