Undermine!

...

Oh, right they're enslaved aren't they? I got nothing.

There are a lot of confusing elements to consider here.

There are two ancient empires of trolls to consider, in the Amani Empire and the Gurubashi Empire. Both of these tribes banded together to fight against the A'qir in the ages before the Sundering. The Gurubashi eventually declined due to angering Neptulon, while the Amani were driven down through wars with the human Arathi tribes and later the High Elves.

Zul'Aman and Zul'Gurub are the capitals of those two ancient empires, respectively. "Perhaps something has happened to once again call for the unity of the disaffected tribes." -- This could mean that the remnants of the Amani and Gurubashi tribes are either a) rallying to fight against the Twilight's Hammer or b) JOINING the Twilight's Hammer and the Old Gods in a bid for world domination.

"Perhaps a certain tribe with allegiances elsewhere sees this as a very bad thing." -- This could mean a couple different things too: Clearly, the Darkspear Tribe has their allegiance to the Horde, and the actions of the Gurubashi/Amani affect them greatly.

But it could ALSO refer to the Zandalar Tribe. They control Zandalar Island, the cradle of Troll civilization, were fighting against the forces of Hakkar in ZG and the Sunken Temple. They were also on hand to document the downfall of Gundrak. And it's Zandalar emissaries who compel the Horde and Alliance to enter ZG and ZA in 4.1. What's unclear here is who the Zandalar owe their allegiances to aside from King Rastakahn.

I don't expect the Zandalar are going to go bad -- in fact, I really expect the Zandalar are going to employ us to fight their war AGAIN, because Jin'do and whoever's running things in Zul'Aman 4.1 are teaming up with the Old Gods.