Even as early as Chapter Six of Lord of the Flies there are indications of the breakdown in leadership. For instance, after the beast has taken a physical form for the boys and become more real to them,
Ralph took the conch from where it lay on the polished seat and held it to his lips; but then he hesitated and did not blow. He held the shell up instead and showed it to them and they understood.
And, Piggy, too, has his prominence and that of rationality symbolically diminshed as he "took off his damaged glasses." Jack challenges the use of the conch and Ralph's leadership as he shouts "We don't need the conch!" but, after Ralph convinces the boys that the fire is the most important thing, the boys rejoin Ralph's side.
Then, in Chapter Seven, the sinister emergence of the sadistic Roger threatens civilized behavior, and Jack becomes more dominant as Ralph himself becomes involved in the hunt for the pig:
"I hit him all right. The spear stuck in. I wounded him." He [Ralph] sunned himself in their new respect and felt that hunting was good after all.
Jack leads the group up the mountain in the next morning to find the pig that Ralph has hit. Again an "impervious Roger" appears and sits by Ralph, tapping the log on which they rest after climbin the mountain. Then, in Chapter Eight, Jack challenges Ralph's leadership again, telling the boys that anyone who wants to hunt can come with him. Finally, in Chapter Nine, the contention between Jack and Ralph reaches its height as Jack and Ralph argue about possession of the conch and the boundaries on authority. Simon comes down the mountain to tell the others that the beast is within them, but is killed, and Jack steals Piggy's symbolic glasses. For the most part Jack has control, but in Chapter Eleven Ralph takes control one last time as he manfully reminds the others with him why they need a rescue fire, leading them to try to regain civilization.
In this chapter, Jack and the others have been liberated "into concealing paint." Jack blows the conch and the boys congregate. However, with the savage killing of Piggy as Roger sadistically sends the pink granite boulder careening down upon Piggy's head. This is the climax of the novel, and the point at which Ralph completely loses any leadership.