Vanilla WoW servers follow Vanilla style WoW expirience, those servers are easy to customize and have low PC requirements, which means population is usually high since anyone can join and play.
History of Vanilla WoW servers
Vanilla WoW servers are the oldest still existing classic WoW servers. With more than 5 years of history Vanilla WoW got a lot of traction and players.
Why play private Vanilla WoW servers?
Levelling up in Vanilla Wow takes quite a long time. For most people the average time it takes to get to 60 level is about two months. The difficulty in the amount of time it takes to progress through Vanilla WoW make each accomplishment really mean something to you.