The word "tenuous" is an apt choice to describe the civilization of the island. Even before the complete collapse at the novel's end, there are a few significant challenges to and failures of the rules set up to maintain order on the island.
One of the first rules to be flouted is about the location where the boys relieve themselves. The agreement is that they will use a rocky area so as not to contaminate water and food sources. Though this rule is essential for the common good, some lack the discipline to follow through and demonstrate no shame for their selfish and thoughtless actions that imperil everyone.
The rule about keeping the signal fire going is eventually broken. Jack is the culprit, and his actions constitute a major setback that angers Ralph and frightens Simon when he realizes that the growing resentment Ralph and Jack have for one another is a threat to all.
The rule of having to have the conch in hand to address the group in meetings falls by the wayside as the boys talk over one another. When the conch is broken at the same moment Piggy is killed, their tenuous civilization is symbolically and literally shattered.