His goal from the beginning was to control the group

Since the beginning of the novel, Jack prioritized being the leader of the group. He resented Ralph and the other boys because his attempt to convince the boys he was best fit to be the leader failed. Ralph appointed Jack as the head of the hunting tribe, hoping to ease conflict, but Jack's jealously and hatred already divided the group from the start. As the plot progressed, he became horrifically obsessed with rulership over the island, undermining Ralph and his abilities every chance he got. Jack’s obsessive behavior started to develop further when he began to challenge Ralph’s authority over the island. When the boys are discussing who will go up the mountain and find the beast, Jack declared he will go and yelled to Ralph “coming?” Jack clearly asked to mock and challenge him, because he didn’t believe Ralph would go up the mountain. He thought Ralph was too scared to face the beast and he would be able to prove he should be their brave and courageous leader. He manipulated Ralph to take control from the him and lead the group, using fear and intimidation to gain the groups support. He even promised them to take them on a hunt if they join his side. Jack eventually gets what he wants and becomes chief, however his power is through fear rather than respect. If Jack wasn't so extremely power hungry, the group could have been rescued when the ship passed the island in Chapter 4, and Simon and Piggy could have lived.

[P1] The only way he wanted to lead was through fear and intimidation.