Ralph was chosen leader by everyone and Jack did not like the rules Ralph set.
Jack became obsessed with power and worried more about hunting and having fun rather than being found. Jack took most of the people and made his own separate group on a different side of the island.
Jack and his group invited Ralph and the two people left in his group to come to a bon fire and have a cook out. One of them showed up late and was running towards them. After Jack yelled out "monster" he and his group stabbed him to death like savages. Afterwards they were in shock at what they have done.
Piggy was trying to make peace and Jacks people threw a boulder on his head and killed him.
Jack takes his group to go out into the wilderness and try and smoke out Ralph so he can kill him.
Smoke him out!
Ralph runs from the mob out onto the beach where he falls to his knees in front of a soldier that is there to rescue them and he balls out in tears. As Jack and his group come out of the woods chasing him and see the soldiers there they suddenly froze in shock.