It's the latter, for the most part. The Alliance doesn't really know that happened, and they probably never will unless someone inside Acherus tells them about it. Heck, if you did tell them about it, what would they do? Go to Acherus and search for a corpse? They would be there awhile.
Eternauta asked a pair of questions...
What's the Horde counterpart to the 7th Legion?
I think that would be the Kor'Kron, though it's made up of all Orcs rather than being multiracial like the 7th Legion. I don't think the Horde currently has a direct translation to what the 7th Legion are, but the Kor'Kron would be closest.
You mentioned that, "There is a very real force that's pushing these changes on the Crusade, but I'll let you find out for yourself (if you haven't already.)" How can I find out? It's a quest chain?
It is a quest chain, yes. If you haven't done the stuff in Dragonblight yet, I suggest going through that. Afterwards, you'll need to work through Icecrown until you reach Death's Rise and the Ebon Blade daily quests there. While you're on the daily quest Intelligence Gathering, you have a chance to get a Note from the Grand Admiral out of the chests/trunks you open up. It has a low droprate in my experience, so you might be cracking open trunks for quite awhile. Just do the quest chain that note starts you on, and you'll find out what's up.
I've asked this before - what is the story behind the Sartharion encounter. Why do heroes have to go and kill him in his lair? Aren't the black dragons part of the Accord?
I've also answered this before, but it gets asked often enough that I'll do it again. The story behind Sartharion and what's going on in the Obsidian Dragonshrine is detailed in Night of the Dragon. The Twilight Drakes are a dragon crossbreed made by Sinestra (who you see on the Netherwing Ledge in Shadowmoon), they're a cross between Black Dragons and Nether Dragons. They eat magic (including Dragon magic), are huge jerks, and need to die. Sartharion is watching over a huge mass of Twilight eggs, so we gotta smash 'em.
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