Thrall becomes the Gaurdian of trisfal

Why Thrall is Gaurdian:

The emerald nightmare was getting worser day by day, until the day the cataclysm began. Azhara and Deathwing has began summoning the Old god from the nightmare to world by creating a gateway with in the maelstrom.

With the Nightmare out of control and an old god about to be summoned Malfurion got desperate with in the nightmare and went back to the world in search of help. Malfurion found a group of people who fights the old gods and their minions exclusively, the new council of trisfal.

Realizing that they have no gaurdian and that them alone can't stop the old god from being summoned. Malfurion looked for a person who has great powers over the elements. Then he found Thrall, a wise leader and a powerful shaman. He tells Thrall that he's the worlds only hope and introduces him to the council.

The council shared there powers with Thrall and he becomes extremely powerful, having the ability to move waters or even open the sea to half. With Thrall on charge in Azeroth Malfurion comes back to the Nightmare to battle the horrors with in it once more.

1k Needles explanation:

Before the events of the cataclysm Thrall was abducted on his way to Theramore for a mission of peace. After being rescued by the goblins who escaped deathwing Thrall ensured that they will have a safe place with in the horde.

After the events which includes Malfurion, Thralls first action was to Take the water out of central Kalimdor so civilization could be built once more.

Thrall found a container for the extra water within the world, but to do it he needed the help of the goblins. He ordered the goblins of Gadgetzan to build a damn so the flood water can fill the thousand needles and parts of Feralas. After the dam was built Thrall moved the flood water successfully.

Areas that are also low will remain flooded due to the "left" overs of the big tidal wave, these areas are dustwallow marsh, swamps of sorrows and the wetlands.


The Expidition to the Great sea:

The new council of trisfal traveled to the great sea but deal with its afairs but they needed help of the alliance and the horde but only the strongest ones was chosen meaning they must prove there selves first in the old world.

With Thrall and his effors in the great sea, there wont be any battle grounds in the great sea. And you kinda dont really need siege engines under water.....

rumor taken from http://www.mmo-champion.com/general-discussions/ulduar-globe-cairnes-death-and-thrall-as-gaurdian-pre-cataclysm-event/msg1310069/