I never understood why the Blood Elves sided with the Horde permanently. They had a lot mroe beef with them, even with Garithos, one general in the entire Alliance. It'd be like if the Muradin's dwarves left the Alliance because of Arthas.
they had way less beef with the horde than the alliance.
Humans: Gary and Arthas, the Belves hold the alliance responsable for both of them.
gnomes: no issue. Arthas decimated human kingdoms too.
Draenei: enemies since the Belves were still under Kael while he was messing with the Draenie
Dwarves: actively spying on the Blood elves and got caught
Nelves: invaded their lands as a hostile force while they were trying to recover from the scourge and broke their buildings (supposedly).
Worgen: no real issue
pandas: no issue
Orcs: burned their forest once.
trolls: no issue had zero contact with them prior to joining the horde
tauren: no issue zero contact
goblins: no issue
forsaken: recieved multiple kinds of aid, then had their obligations to the horde hammered home to them in a short story
pandas: no issue
Orcs: Attempted to invade their land and almost succeeded, burning down their ancient trees and killing quite a few elves. Kael was pretty mad about the trees.
Trolls: While never having encountered the Darkspear specifically, elves and trolls have a very long running racial feud. Some blood elf npcs are racist towards troll players.
Tauren: No contact.
Forsaken: Their citizens are rather suspicious of them and Sylvanas, but didn't have much of a choice.
Goblins: Fought them during the second war, don't think too highly.
Humans: Have had a very long alliance with them, have been working with them for centuries sense the troll wars. The humans saved them from the Horde no less.
Dwarves: Had petty racial squabbles, but no major wars or anything to the extent of troll-elf.
Gnomes: Little contact.
Nelves: Tyrande and Kael had a decent friendship and they helped each other out. They were exiled a thousand years ago.
It doesn't make too much sense on why they would suddenly abandon their ancient allies so easily. Sure, Garithos was mean to them but he was one general.
Not to mention the blood elves had rather close ties with the Kirin Tor, and they joined the Horde before it went neutral.