The way the children behaved in the later half of the novel was far from civilized. They are easily convinced to go against their past way of life. From the beginning of the novel, the boys have trouble uniting. There are several attempts at trying to run the island in a civilized manner, but it all falls apart very quickly.
Humans are tempted quite a lot by their uncivilized nature. Most of us know the difference between right and wrong, need and desire. It is strange that even though we are aware we are doing something wrong, we still do it. Almost always, we seem to choose our desires over our needs. At the end, the boys are split up in to two tribes. One symbolises good and the other, evil, the smaller one being the good and the larger one being the evil.
In a way the method they govern the island is like our normal society these days.
Everything is just happening much quicker than it does in real life. Governments do get overthrown and there are always wars going on between humans. Right at the start, they democratically pick their leader. They commit themselves to obey the leader's orders. The system starts to collapse and the government, in the end, is overthrown. Others take control and there is war between the two divided tribes. It symbolises our supposedly perfect system.
At first the boys are happy with Ralph as their leader, but in the end they are persuaded by Jack that he would make a better leader. This is because Jack can fulfill their desires and Ralph can't. Ralph wants what is better for them not what they want. At the beginning everyone seems to understand that, but is lead astray by Jack.