https://wowwiki.fandom.com/wiki/Alterac_Valley
[Patch 2.3.0] (13-Nov-2007):
All Warmasters are linked to each other and their respective Generals and can no longer be pulled individually.
It wasn’t changed until burning crusade.
Xrealm matchmaking was only a few months at the end of vanilla itself.
If anything, they should just keep it to per realm instead, thus making the pools so small that premades would be possible for both sides.
The mechanisms of gigantic matchmaking pools only makes it possible for the smaller ones, unfortunately.
Also, this “everyone vs. everyone” size of the xrealm matchmaking was NEVER in vanilla.
The battlegroups in vanilla looked VERY different once xrealm matchmaking became a thing.
https://web.archive.org/web/20070206055244/http://www.wow-europe.com/en/info/basics/battlegroups.html