Why does Jack gain the power fight against Ralph? Why does he system gain the upper hand?
Jack wins over the boys because he sets goals and achieves them. First, he tells his hunters that he will protect them from the beast. After they kill Simon, he tells them that it was really the beast, not Simon. So he takes away the shame that they would have felt. Then he protects them by having "guards" around castle rock. He has an army of boys now. They paint their faces and have fun. They hunt. They rule. And when they need a fire, they STEAL Piggy's glasses. That was a goal for them as well, and they succeeded in grabbing them from him and taking away not only his physical vision, but the vision of common sense and intelligence.
Ralph is losing it by chapter 10, and he can't even remember why they need the glasses or fire. Jack is in full control and is very confident. The boys are loyal to him more out of fear than anything. He beats those who do not listen or follow his way. He is the ultimate dictator of his group. At this point in the story, the boys don't want to make shelters and watch fires. They want to play "hunters" with a leader who has a plan.