It was a truly sinister scheme. The Golds were just doing what they could to survive, realizing that they had been screwed over once again.
If they just waited, with their lack of natural defenses, it was inevitable that they would suffer. They had no idea who was in the direction they were going, but if they came across Theron's fortress, a fight would inevitably ensue.
It didn't matter if they had a common enemy or not. Fighting was the only option.
Although there was potential for an alliance to be struck, the Gold Clan had simply lost too much. They needed a victory—a real victory.
Still, the main reason that an alliance was impossible was because of the risk the Gold Clan was taking at this very moment. They had all but abandoned their fortress and were setting out. They would probably even start attacking the moment they ran into Theron's scouts, and by then the trap would already be laid.