One of the possible explanations of why things (like peaceful society) "break up" is the absence of law and order. When laws exist, people refrain from committing wrong actions (crime) partly because they are fearful of the punishment. However, in the island, there is no one to administer punishment effectively, which means that people disregard the rules that were established, and therefore, society appears unsuccessful.
One example in the text is the fact that Ralph and Piggy are initially very concerned with the rules they have established, such as keeping the fire going. However, since there is no punishment for those who do not care, and instead, this is a responsibility, Ralph and Piggy are tempted to forget about this important task. Another example is the fact that the children behaved relatively well when living with their parents, as the parents and society disciplined them. However, they commit terrible acts when they are in the island, as they cannot be punished.
An example in real life is the case of criminal justice. In general, countries where police and the criminal system are effective have lower crime rates than countries where criminals know they can easily get away with their actions.