What circumstances, events, and psychological forces cause the deterioration?

The deterioration of civilized behavior? Civilized behavior is hampered by a lack or rules and authority. When the boys begin to fight between themselves and go their own ways, we become succinctly aware of changes in behavior and expectations. Survival means one thing to Ralph, Piggy, and Simon...... and another to Jack and his hunters. The littl'uns just want to be cared for..... they want to play, and eat, and be protected from the beasty above all else. Ralph wants to be rescued, as do those who follow his lead. The break between Jack and Ralph is the beginning of the complete deterioration of the group as a whole. Jack supplies meat.... instant gratification. Ralph asks for cooperation and work. The rest of the boys gravitate toward Jack because he gives them what he promised..... and what they need.