During the Burning Legion's third invasion, the Knights of the Ebon Blade traveled to the Shadowlands to acquire the Aggregates of Anguish, five tormented essences of powerful souls - Admiral Proudmoore, Soulbinder Nyami, Grand Empress Shek'zeer, Grand Apothecary Putress and Archmage Arugal. Salanaar required these to conjure the Steeds of the Damned for the order's new Horsemen.
Since this was an early questing experience and not an endgame one, I didn't get much sense of how Covenants—Shadowlands' new Order Hall, Garrison, or War Campaign-like systems—work. Neither did I have much time to dive into the story, though I saw enough to know that, if you like the flavor of the recent WoW expansions, you'll probably like this one, too. (I, for one, am glad we're going to get a brief respite from the Alliance vs. Horde war storyline.)
After rumors about this possibility for the last several expansions, Blizzard has finally followed through on a level crunch. Whereas characters in the current Battle for Azeroth expansion cap out at level 120, the cap in Shadowlands will be 60—just as it was when the game first launched and just as it is in World of Warcraft Classic. Level-120 characters will be scaled down to level 50 when Shadowlands launches.
Claim a covenant's power: players will be called upon to forge a bond with one of four covenants that rule Shadowlands' new zones, setting the tone for their journey through the expansion with a full covenant campaign. As they level up, they'll get new abilities based on their choice, including class-specific abilities for each Covenant—as well as developing soulbinds with specific covenant members, which grant them access to that character's specific traits and bonuses.