Causes of the invasion
The Cataclysm has caused the gates of the Greymane Wall to shatter, which marked the end of Gilneas' isolationism from the rest of Azeroth. Due to the events at the Battle of Angrathar the Wrathgate, the Forsaken are "in the dog house" with the rest of the Horde and the Horde leadership, now controlled by Garrosh Hellscream, has ordered Sylvanas Windrunner to claim Gilneas so the Horde can have a port in southern Lordaeron.
Ships of the Forsaken Navy commenced a bombardment of the coastal town of Duskhaven and its surrounding farmsteads while landing footsoldiers. Newly cured worgen, acting under the command of Prince Liam Greymane, moved into action, catapulting onto the ships and slaying their captains, and then leashing a pack of mastiffs on the area commander, Dark Ranger Thyala. But even with this victory, there came a price. The earth, already weakened from the bombardment, began to fragment and collapse as the Cataclysm continued, and an evacuation of Duskhaven was put together before the town was completely consumed. The survivors fled to Greymane Manor, and then further inland - into the Blackwald.
Origins of the Curse
Within this dark forest, the Gilneans met the night elves, who told them of the origins of the worgen curse - that long ago, the Druids of the Scythe had abandoned the balance and allowed the beast within to consume them. They had been banished to the Emerald Dream to sleep for eternity under Tal'doren, the wild tree in the Blackwald...but not before their curse had spread. Lord Darius Crowley, who had also been transformed into a worgen and had managed to regain the balance between man and beast, revealed that the Forsaken were not only after the lands of Gilneas, they were after something that could bring the worgen under their control - the Scythe of Elune. Aided by Tobias Mistmantle and his trackers, the worgen killed Sylvanas' dark rangers and reclaimed the precious artifact. Knowing that the alchemy that had returned their minds to them would not last long, the worgen drank of the waters of Tal'doren, and restored the balance between human and beast. King Genn Greymane himself came to the Blackwald and revealed that he too had been affected by the curse, and joined with all of his people to drive the Forsaken from their lands.
Lord Godfrey was an unaffected nobleman who condemned the transformed Gilneans as monsters. Upon learning that Greymane himself had been cursed, Godfrey put a plan into motion that he believed would save Gilneas. Joined by two eastern lords, Baron Ashbury and Lord Walden, Godfrey captured Greymane and held him prisoner. He hoped that by turning the king over to the Forsaken, Gilneas would be spared.
The Gilnean worgen struck back, tracking down and assassinating both Ashbury and Walden, and cornered Godfrey at Tempest's Reach. With his support gone and his plan defeated, Godfrey committed suicide rather than acknowledge a worgen as his king.
The Battle for Gilneas City
With the dissent from within crushed, Greymane sent his loyal supporters to aid in liberating the mining town of Emberstone Village from Forsaken control. Prince Liam and Lorna Crowley, the daughter of Lord Darius, led the troop, making headquarters in the livery stables. After freeing the enslaved Gilneans, they aimed at the Forsaken leader, Executor Cornell, known for his unbound ruthlessness, and Valnov the Mad, the so-called scientist who carried out inhuman experiments on the villagers too old to work the mines.
Having assembled an army composed of every available Gilnean, the army was split around Gilneas City, Liam heading the assault from this gate, while King Greymane and Lord Crowley handled the assault on the other districts.
Liam caught Sylvanas' forces at Greymane Court, while his father met them on the other side. As the tide was turning against Sylvanas, she used her dark powers to stun every one in the immediate area and aimed a poisoned arrow at Genn Greymane. Liam jumped in front of the bowshot, saving his father from certain doom. As Sylvanas fled the scene, Liam died with the knowledge that the city had been freed from Forsaken control.
Escape from Gilneas: The Endgame
Later on, Sylvanas met with General Warhowl, envoy of Warchief Garrosh Hellscream, telling him that Gilneas was under control and agreeing not to use the Forsaken Blight, as its development had been banned after the incident at the Wrathgate. As the emissary left, Sylvanas told High Executor Crenshaw to deploy the new plague as planned, despite Garrosh's command.
At the dawn of the next day, despite the wishes of Garrosh Hellscream, the Forsaken used their Blight on Gilneas, what the Forsaken didn't know however is that the population was being evacuated through a secret passage to Aderic's Repose due to Tobias Mistmantle and an Adventurer discovering the plot. While Adventurers distracted the Forsaken using bombing bats they had recovered destroying some of their Blight deployers and thinned out the forsaken ranks, the rest of the city populace escaped.
The night elves, led by the Priestess of the Moon, Belrysa Starbreeze, made good on their promise and brought ships at Keel Harbor, as well as an offer of sanctuary in their lands. Unfortunately, the Forsaken's allies, the Horde, arrived as well. An orcish gunship, similar to Orgrim's Hammer, which had fought in Northrend, entered the field, preventing the transport ships from taking the Gilneans to safety. While the druids were holding the enemy back, the siege weapons carried by the elven ships were deployed and met their enemy head-on.
A hippogryph-mounted party boarded the gunship to place explosives in the engineering room below deck. As they proceeded, the gunship's captain, Korm Bonegrind, appeared and the party fled on wyverns roosting on the lower deck. With its engines destroyed, the explosives detonated, destroying the gunship at the Greymane Wall.
The liberation of Gilneas
After the Gilnean civilians were evacuated to Darnassus, Greymane went to Stormwind to ask for support for his people. Realising that accepting Gilneas into the Alliance would grant them strategical allies against the Forsaken, King Varian Wrynn sent the 7th Legion to Gilneas. At the same time The Gilneas Liberation Front made allies with the Bloodfang pack lead by Ivar Bloodfang who helped the GLF attack the Forsaken front toward the north, cutting them off from the forces in the city. To add to the combined strain on the Forsaken, the hundreds of survivors who had fled Southshore and Hillsbrad Fields when the Forsaken attacked them too had invaded Fenris Isle and claimed it as their own lead by Magistrate Henry Maleb. Desperate for revenge on the undead monsters, Darius Crowley and Ivar Bloodfang offered the people a chance to protect themselves by becoming immune to the plague by drinking the blood of the Worgen and having the strength to get their revenge. This single act bolstered the Worgen numbers greatly and although forsaken adventurers managed to kill many, it barely made a scratch in their forces.
As most of the forsaken forces were occupied fighting the Worgen, the 7th Legion fleet, sent by king Varian Wrynn sank down the entire Horde fleet with Gnomish submarines and invaded the City. With the Warchief's fleet destroyed and most of their forces cut of by the Gilneas Liberation Front, the 7th Legion took control of the capitol and killed all the Forsaken troops in Gilneas City leaving only their commander Captain Rutsak alive to witness the massacre. After that the combined forces of the Gilneas Liberation Front and the 7th Legion took control of Gilneas, finally free of the Forsaken. As the Forsaken retreated, adventurers managed to recover the body of Vincent Godfrey and assassinate the 7th Legion's commander, Pietro Zaren, while others forces managed to retrieve the bodies of Baron Ashbury and Lord Walden. After that the Forsaken forces had retreated back to Silverpine Forest and the Gilneas peninsula where they had made their last hold out in Gilneas
Gilneas was left in ruins, both by the Forsaken invasion and by the very land ripping itself apart. While their soldiers in the front, the surviving Gilnean civiliences fled to Teldrassil and other Alliance strongholds, where they offered their services to the Alliance. With his homeland turning in to a war zone and his heir slain, Genn Greymane journeyed to Stormwind, political and military capital of the Alliance, where he stands at the side of Stormwind's master, King Varian Wrynn.
The Invasion of Silverpine
Now that Gilneas was secure the 7th Legion and GLF attempted to begin pushing into the lands of Lordaeron and reclaim it from the Forsaken. Meanwhile Sylvanas Windrunner had Arthura bring back Godfrey, Walden and Ashbury in service to the Forsaken. Out of survival, the Kirin Tor mages of Ambermill and Dalaran Crater (left behind to protect the land for the day when Dalaran would return), made a pact with the Alliance to protect themselves from the Forsaken who in the past years had been attacked by them. They agreed to summon the Stormwind army when the time was right in order to repel the Forsaken. To protect themselves till then, they phased the entirety of Ambermill out of their reality so they could not be attacked. This plot however failed when Forsaken adventurers found a way in and disrupted the connection to the different dimension and brought it back into the original. At this point the Forsaken killed the Kirin Tor mages and brought them back as New Forsaken.
The Forsaken than began the destruction of Pyrewood which the Alliance were in control of, which was then set ablaze. The 7th Legion and Gilneas Liberation Front then decided to begin their plans and start the invasion of Lordaeron. The two armies clashed in southern Silverpine. As the battle went on, Sylvanas sent Godfrey and his entourage to capture Lorna Crowley who had not become a Worgen and could be changed into a Forsaken. She was overpowered and kidnapped by the traitor Godfrey and brought back to Sylvanas where she could be used to finally put an end to the invasion. Accompanied by High Warlord Cromush, her Val'kyr and her most trusted soldier, they went to meet Darius Crowley and Ivar Bloodfang at the gates of Gilneas. There she offered Darius a choice, leave Silverpine and take the entire GLF with him, or stay and his daughter would become a Forsaken. Godfrey, Walden, and Ashbury then appeared with his daughter for him to make an ultimatum. Unable to allow such a horrifying fate happen to his daughter, he agreed to retreat back to Gilneas. Lorna was released and Ivar cursed Darius for being a coward.
As the three fled back to the safety of Gilneas, Godfrey did the unthinkable and assassinated Sylvanas Windrunner. In shock, the Horde group had a short duel with Godfrey's trio until they were overpowered and forced to fall back to Shadowfang Keep. Cromush ordered the Val'kyr to "fix" the Banshee Queen but in doing so they sacrificed themselves in the process to bring her back. The Dark Lady rose again furious with rage at Godfrey's betrayal and believed that the Val'kyr were indeed the future of the Forsaken. With that, she returned to Undercity to recover. The Alliance forces fell back to Gilneas and the invasion of Silverpine was over.