The Trade Wars (or cartel wars) were conflicts that happened on the island of Kezan, fought between various goblin cartels. The exact time period they occurred is unknown, though Druz fought in them, and Ziya was a child during them. There were at least four Trade Wars and were followed by the Peace War, which was supposedly even worse.
The Trade Wars didn't have very defined front lines, with combat occurring in tunnels and storerooms throughout the Undermine. "Ambushes" consisted of enemy goblins kicking down walls. Jastor Gallywix's favorite bakery was destroyed and rebuilt over the course of the multiple wars, and finally melted during the Peace War.
The conflict that emerged after the Liberation of Kezan between the goblins is possibly the first of the Trade Wars.