Both stories obviously represent the dark side of ambition. In Lord of the Flies, Jack's reaction to finding out that there can be rules and he can enforce them with punishments demonstrates that he just wants power.
“We’ll have rules!” he cried excitedly. “Lots of rules! Then when anyone...
breaks ’em–” (ch 2)
Jack fights Ralph for power in a more direct way than Macbeth fights Duncan, but the result is the same in that Jack creates his own little kingdom out of the choirboys. Malcolm creates an army from his supporters that flee because of Macbeth.
Macbeth does not want to be king at first. When the witches tell him he will be Thane of Cawdor and then king, he seems to think this will be real.
The Prince of Cumberland! That is a step(55)
On which I must fall down, or else o'erleap,
For in my way it lies. (Act 1, scene 5, p. 18)
Nevertheless, Macbeth does wan t to be king. He decides that if he is not named king, he needs to take the throne himself. When Jack is not chosen leader, he too decides to make himself leader.