This is a great question. 

The whole book can be seen from the perspective of power. At first power was accorded to Ralph as he was a natural leader. The boys followed him to organize camp and to plan a way to get rescued. 

As the book progressed, Jack became a rival leader. This was due to the delay of rescue. He represents the chaos. The struggle between the two boys is about power.

We can also say that there is a struggle between Piggy and Jack as Piggy represent science. If you recall he is the one who makes fire and call people to order with the conch shell. 

In a word, power struggles are all over.