The War begin with an attempt by the Sindar Elves of Quel'Thalas to take control over Silvermoon city but they were repulsed and from this point on they were constantly pushed back by the forces of the Lothlorians. Towards the end the forces of the San'Layn attemted to take control of the Sunwell, and held it suprisingly for a great period of time, until they too were pushed out by the Lothlorians.
At the conclusion of the civil war it would lead to the founding of two new kingdoms, in San'Layn, and Quel'Thalas, while the forces of The Kingdom of Lothlorian continued to grow in strength, and had basically solitified control over the entire forest of Athel Loren.
The civil war in Lothlorian began because the once unified foundation of Lothlorian had become mired in three seperate entiities.
Main Article : Kingdom of Quel'Thalas
The first were the original members in the Quel'Masi Elves, these Elves were true Sindar Elves, and wanted nothing more then simply living in peace with the forest, and ignoring the continued push of the royalty to move towards a heavy amount of Magi use. This difference of opinions reached such levels that the royalty of Athel Loren begin sending more and more of the Quel'Masi Elves to their expansion forest of Quel'Thalas, where they were allowed to live however they wanted.
Due to the nature of the Sindar Elves, they reproduce far less then the Lothlorian style of Elves meaning that over the centures of existence they fell from 100% of the population to less then 40% by the years before the civil war. This was even more starke when you take into account that they were only 17% in the Athel Forest itself, with the vast majority of their people in Quel'Thalas.
Main Article : Kingdom of Lothlorian
The second group within Athel Loren were the Lothlorian Elves. When Illidan had planted the seeds that would eventually found the Sunwell, the Lothlorian Elves was the name given to the Elves that listened to the words of Illidan and used the Magi of the Sunwell. At the time this was a rude thing to call them, but as their numbers have dramatically increased they are now called this out of routine, and it is no longer insulting.
The Lothlorian Elves really came into being when the High King of Athel Loren came to be a Lothlorian Elf due to his use of Magi. This was the moment most can point to and say that was when the Lothlorian Elves had become the dominent force in Athel Loren. Most of the important areas including the massive city of Silvermoon were nearly completely under the control of the Lothlorians, and this was especially true for the military where nearly 70% and growing of the Athel Loren forces were Lothlorian Elves.
Main Article : San'Layn
The third and final group were the San'Layn Elves, and if any distinction was needed it would be with the Dark Elves. The San'Layn were basically hard core Lothlorian Elves who had absolutely no morals or ethics and all they wanted was more and more knowledge of the Magi. The San'Layn began as a small organization with the Lothlorian Elves but they slowly begin to become their own minor society that was distinct and seperate from the overall society.