The first level 1 mass raid occurred only two months into the Beta.
From the WoW Archivist:
The first class protest in WoW occurred only two months after the game launched. Like Druids United, the problems stemmed from beta changes – the original WoW beta. Warriors received some substantial nerfs late in the beta life cycle. The beta nerfs already had warriors grumbling. Then further nerfs to the class were patched in to the live game not long after launch. The official forums exploded with complaints.
With Blizzard showing no sign that they would revert the changes, warriors planned a protest on the Argent Dawn realm for the night of Friday, January 29, 2005. All protesters were encouraged to roll a level 1 gnome on Argent Dawn and march to Ironforge. The protest had several names, but the one that stuck was the Million Gnome March.
As the event began, organizers created a guild on the Argent Dawn realm and invited protesters into it. So many attended that the guild interface couldn’t handle all the invites – the invite button stopped functioning.
Gawkers and Argent Dawn natives showed up at the event too. Some asked the protesters to leave the realm. Some taunted them. Others just wanted to see what would happen.
Blogger Foton reported on the event live: “They are about to begin the march to Ironforge. It is a sea of naked gnomery, and I cannot adequately describe how horrifying a vision that is.”
This event inspired the Blackrock raids that plagued Argent Dawn throughout Vanilla. Hogger raids would eventually occurs as well, before the level 1 “running of the bulls” would start occuring with Tauren running from Thunder Bluff to Orgrimmar.