The Goblin Invasion happened during the Quest for the Keys of La-Ariel.
It ended about three and a half years ago. 1011 P.A.
The Galadrians threw every thing they had at the Goblin Army, but were overwhelmed by the sheer numbers involved.
The Goblins had no way to support or feed an army that size in the field. As the war progressed, the advanced went from orderly columns to endless streams of small bands of Goblins who were racing each other to be the first to get to fresh supplies of food. The Goblins ate everything edible, including fallen defenders and their own dead. Desperate, Starving Goblins stripped the landscape like locusts leaving bare, toothmarked debris in their wake.
The Goblins only had one way to go - to turn around was to guarantee a grinding death by starvation. To turn aside was to guarantee divine wrath.
Refugees and retreating survivors flooded into the Capital city of Gala. The walls were reinforces and manned. The Defenders were grim. Although attentuated by horrible conditions, the Goblins outnummbered the defenders badly. The Goblins had to win, or die.
The Goblins beseiged Gala but did not take it.
When the Climax of the Quest for the Keys occurred, the Goblin God was revealed to be a fraud. He was defeated and destoyed.
The Goblin reaction was psychotic. They rioted and mass murdered each other. Although a few bands tried to press the assualt and express their rage against the defenders, most Goblins just lost their minds.
Stunned scouts from Gala discovered that the unhinged Goblins fell on each other for food. The Goblins routed themselves and fled pell-mell in all directions. Subsequent goblin-to-goblin encounters ended violently.
The Goblin withdrawl, as such, was to flee generally southwards towards the Iron mountains. Small bands would battle other small bands and then survivors would eat the dead and keep fleeing.
No one knows what percentage of the Goblins were casualties. In terms of regional politics and history, the effective answer is "All of them."
Isolated small bands are occasionally encountered. Galadrians tend to exterminate them with Extreme Prejudice