The Trade Coalition is the goblins' merchant empire, and is ruled by all five of Undermine's trade princes. It is huge, far-reaching and massively complicated. It commands the Trade Fleets. The Trade Coalition condones smuggling and slavery. Undermine contains the headquarters of the Trade Coalition.
The Trade Coalition has little influence over Revilgaz, and indeed the Raiders attempt to go under, above, or around the coalition's head. Goblin barons are allegedly there to serve as magistrate over the land and holdings owned by a trade prince.
The five (more or less) trade princes collectively control the Trade Coalition. Run by Undermine's trade princes, the Trade Coalition controls much of the commerce throughout the world. Trade Prince Steamwheedle, the richest known goblin on Azeroth, runs the shipping division practically on his own.