The primary event which led to Piggy's death in the novel Lord of the Flies occurred when Jack stole the larger boy's glasses during the night with the aid of the hunters. It is the theft of the glasses which spurs Ralph, Piggy, Sam, and Eric to journey to Castle Rock, the location of Piggy's death. Piggy and the other boys probably would not have risked traveling over there, if not for two reasons:
1) Piggy's vision is extremely poor, and he cannot function on the island without the aid of his glasses.
2) Ralph's insistence that the boys had to continue making the signal fire so they could be rescued. The glasses were the only means of making fire on the island, and without them, Ralph feels that the boys will never be rescued; they will be doomed to stay on the island forever.
Once at Castle Rock, Piggy takes the conch in hand and makes a plea for the good of civilization and the return of his glasses:
Which is better—to be a pack of painted Indians like you are, or to be sensible like Ralph is? . . . Which is better—to have rules and agree, or to hunt and kill? (Ch. 11)
He unfortunately sets himself up as an easy target for Roger to destroy with a well-aimed boulder. Piggy's tragic end comes as a result of the building acceptance of savagery and violence on the island.