Once Macbeth kills Duncan and becomes king, he experiences a sense of paranoia, a fear that his throne, his crown will be challenged or taken away by various people. He is also thinking of the witches prophecy. Remember, he goes to the witches a second time, for more information about his future. Some of the prophecy he does not understand.
He suspects that there are members of his kingdom who want his crown, so he murders them before they get the jump on him. He murders Banquo and Fleance because the witches told him that Banquo would be father to kings. Macbeth gets rid of them in advance of Fleance challenging his crown, except Fleance escapes the murderers.
He sends murderers to kill Macduff, because the witches told him "Beware Macduff," except he is not home, so the killers slaughter Macduff's family just for insurance against Macduff thinking he should ever turn against Macbeth.
Macbeth continues to murder to protect his power. He took the throne through violence, so he fears violence will overtake him and seize his crown, since he is not a rightful King. His succession is false, Malcolm, the older son of King Duncan is the rightful heir to the throne. Macbeth knows that he will have to fight to keep his crown.
Killing Duncan was the primary aim of both Macbeth and his wife. Because, Macbeth had a keen ambition to gain power. And when the witches equivocated, he took them too seriously and already, along with his wife, began plotting to murder the king. In order to ascend the throne, he assassinated the king first. Then to secure his kingship, he kept murdering more. Because he thought: "To be thus is nothing, / But to be safely thus", (act 3, scene 1). So, for ensuring that his path would be smooth toward the throne, he killed Banquo, who was prophesied by the "weird sisters" that his children would be successor to the throne, and later murdered Macduff's son.
It is Macbeth's ambition and gluttony which led him to accomplish such butcher-like acts. When a man gets involved in such deeds once, it is difficult to overcome his greed and return from the hellish path. Similar thing happened in the case of Macbeth.
In my opinion, it's because he's a soldier. In battle he only needs to do one thing kill the guy's on the other team. Whenever, he is confronted with a problem he does what he knows best he tries to get his enemy killed. Also, He is paranoid after gaining control of the throne and wishes to hold on to his power.
First Off he is pissed that Banquo's Sons will become kings(he later sees the apparations of the 8 kings in a row symbolizing all of Banquo's sons as Kings) and second he's afraid that Banquo will tell someone that he killed Duncan,so therefore he hires the 3 murders who are in reality losers who dont have anything to lose in life so they take the job and kill Banquo and his son Fleance while theyre out riding,unfortunately the plan backfires when Fleance flees.As for Lady Macduff's castle they were murdered for having to do with Macduff there was no actual reasoning in killing his family.
So no one steals his throne Im a 7th grader
Macbeth is primarily driven by Lady Macbeth to continue committing murder. In her monologue "Unsex me here..." we as an audience see the male/female traditional gender roles being reversed, and ultimately she is the driving force. Upon Macbeth repeating the witches' prophecies to her, Lady macbeth pushes him to eliminate anyone who might stand in the way. It is not until she begins to feel guilt-- the "Out damn spot" scene-- that we see these roles return to traditional gender roles, then ultimately concluding in Macbeth causing his own demise.