The Art Of War: Warrog Edition.

The conflict between the Iron Fur and the sharp tooth pack didn't start and end in a single day. It has been going on for a long time. In that period of time, Sauron had been using some less-than-honorable tactics to weaken the sharp tooth tribe. They are tactics that is usually frowned upon.

He would ambush their warriors when they went out to hunt. He didn't attack them personally so that it wouldn't be considered bullying but he made the warriors of the iron pack attack those of the sharp tooth without any reason. They attacked and killed the paragons of the sharp tooth pack without being officially at war with them.

Those preemptive strikes caught the sharp tooth pack off guard. They couldn't defend themselves against the sudden attack. This way, Sauron reduced the manpower of the sharp tooth pack and also weakened their pack leader.