May as well start out with the forest that the PC's started in and work my way from there. This has been the focal point of my campaign so far, and I have the most info about it.
History
Draligar Forest (200 miles N to S, 350 miles E to W)
The history of this forest dates back three thousand years, before it was elven a forest. The whole place was actually a rolling land, where dwarves held many strongholds on the surface. Beneath the hills were natural caverns where dwarves mined rich ores, even ianry (a magical metal used in the creation of artifacts). For one thousand years the dwarves grew richer and richer.
On the first shift of the day, a dwarven miner started digging at the end of one of the tunnels. In moments, he had opened a small hole in the wall. Peering through, he found a dark elf starting back. The dwarf never had a chance to raise the alarm, nor would he ever find out that he had tunneling into the dark elf city of Quasiet'inal, near the Yzintek Monistary (an order of dark elf monks / fighters). By the end of the first shift, the dwarven mine was overrun by the silent, deadly dark elves. Within the week, all except one dwarven mine remained. The mine the dwarves name Numeth'ador (dwarf for impentitrable maze).
As the dark elves found out, the mine had been well named. With twists and turns every few feet, tunnels in random places with random dead ends, crevasses, sinkholes, and many other dangers, Numeth'ador proved to be fatal for it's intruders. The dwarves launched themselves into a full fledged war, which consumed their thoughts and time for the next four hundred years.
The dwarves pressed the war, which had quickly grown into a stalemate. The dwarves were few, while the dark elves had a nation of trained warriors. By the time the fifth century was rolling around, the dwarves knew that defeat was to be soon upon them. One of the few dwarven wizards at the time, whose name has been lost in the flow of time, suggested an idea to the council of dwarven elders. With heavy hearts, the dwarves agreed to the wizards idea.
The wizard began preparing his spell, while the council selected five of it's fastest messengers (for the dark elves held all the surrounding lands above and below, although the only came out at night above ground, they were still thick upon the land). All the surviving dwarves gathered in the main hall of Numeth'ador and told of what was about to happen. They agreed.
The messengers were sent of, and immediately the wizard cast a spell that sealed Numeth'ador from above ground and below. Two days passed as he wove a spell, and for two days the walls of Numeth'ador throbbed as magic was drawn through them. On the third morning, the wizard finished his spell.
As soon as the last syllable was spoken, every dwarf had his life force ripped from him, empowering the colossal spell. The wizard was vaporized as a large explosion rocked throughout the halls. Hundreds of miles away the explosion was felt, and for two weeks wizards all over the world could only cast low level spells (level 1 to 3) and many said the end of the world was at hand. The drained magic slowly returned.
The explosion ripped over the surrounding lands that had once been ruled by dwarves, leveling every building on the surface. In the moments after the explosive force, another force swept over it, and immediatly plants began growing. In mere moments where hills had once stood, a thick, healthy forest stood. All except the twenty miles surrounding Numeth'ador which became a stagnant swamp.
The dark elves retreated to their cities deeper under the earth, not wishing to lose more of their kind, still unsure of what had took place. The few scouting parties that found a forest where there had been none before, returned with word of the great sorcery that had taken place. The dark elves of Quasiet'inal decided that the surface was off limits, and resumed plans of conquering the under world.
Meanwhile two of the dwarf messengers (two were captured by dark elves, and the third just couldn't get out of the blast area in time) made there way to their destinations. They told two elven kings of the new forest in the south, and what had transpired. Only one of the kings sent a party to see if it was true, the other merely beheaded the dwarf as he expected treachery from the dwarf and his race.
The party returned and told the king that the dwarf spoke the truth. The king released the dwarf, who went to the dwarven nation in the northwest to tell them of what transpired. The elven king saw the forest as a bigger forest, and decided that his people would be better off if they settled it. An exodus began a year later, and within the decade the elves had relocated.
The elves settled the eastern half of the forest, and to their surprise, found a community of forest gnomes living in the north. The elves, outnumbering the gnomes, made a deal with the gnomes, claiming that if the gnomes wished to stay in the elven forest, the gnomes would have to always have 100 gnomes as servants (slaves) for the elves. The gnomes, seeing no other alternative, agreed.