We have sources point out Magni continued sending support for Garithos, Dalaran mages continued support for Garithos and heck even Stormwind nobles sending recourses.
Theramore most likely didn't know of garithoses actions outpost in loch modan and hinterlands weren'y even really active for that. eventhough they didn't do what Garithos did alliance nations still kept supporting Garithos. Also cultural split was in these 3 outpost mostly as not a major source of their population. most helfs and belfs still respected sunstrider family as their rightful monarchs as such as a nation it would make no sense for them to ally with the alliance as trying to execute the last member of your royal family is looked upon well
Well its not the same horde wc2 horde was Blackrock, black tooth grin, Stromreaver, twilights hammer, Dragonmaw, Amani, Bleeding hollow and death knights.
during classic clans which made the horde were Shattered hand, Frostwolfs, Warsongs and Blackrocks remnants from interment camps. As such clanwise differant and lets look at actually responsible individuals during rise of the horde most orcs were artificial made older by fel magic and lets look at two who were children then Maim and Rend blackhand other has died most likely old age and Rend is an old man in classic and lets look at an orc who proper adult during those times drek'thar and check his physical state in cata..... its most likely most blackrock orcs died of old age until vanilla who were responsible.
ps: if go by member count twilight hammer has more members inside alliance with their 2 of their 3 archbishops :P
oh oh and now you are saying mind controlled people are at fault classic alliance..... heck it would easier to blame than on alliance too with Arthas as he was the grown prince of alliance nation.