Regarding this split within the Alliance, the Adventurers from Quel'Thalas and Stromgarde felt the biggest headache.
(Adventurers have racial and national distinctions, with even subtle differences in talents between members of the same race from different nations, such as the Frost Resistance Talent of Altland folks.)
They discovered overnight that they had been expelled from the Alliance.
Neutral forces are not official factions, which means that, in theory, they can't have their own Adventurers. All established Arathi humans and Quel'Thalas High Elves received a system email and three letters from different factions.
Each letter could trigger a faction quest, but once one was triggered, the remaining two would be invalidated.
[System Notification: Your race's faction has withdrawn from the Alliance, and you have now become a neutral Adventurer. Please choose the faction you wish to join and complete the corresponding faction quest to obtain a faction identity.