The War of the Satyr was a conflict fought between the night elves and the former night elves and now demons, the satyrs, seven hundred years after the War of the Ancients. Armies of satyrs attacked the night elves with the intent of destroying their civilization.
At least part of the war was fought on Ashenvale. The satyrs were helped by demons that had somehow lingered on Azeroth after the defeat of the Burning Legion. The night elves were directed by Malfurion Stormrage, Tyrande Whisperwind and Shandris Feathermoon. The night elves Ralaar Fangfire, Belysra and Arvell fought in the war. The former two created the worgen during the war in order to combat the satyrs, by enhancing the pack form.
The ensuing War of the Satyr exacted a heavy toll from the night elves, but ultimately they vanquished the forces that had set out to wreak havoc on their world. The war completely decimated any semblance of central leadership for the satyrs, forcing them to live in small sects to this day. After the war, some druids came to believe that at their core they were wild creatures, their humanoid forms merely a guise. They left night elf society for a forested island and were not seen for thousands of years.
Adapted from Wowpedia