Get revenge. Of course the reason Malcolm wants Macduff to kill Macbeth is because it paves the way for Malcolm to become the next king.
He decides to kill the king.
She tells him that he has to die so MacBeth can become king.
The witches only gave Macbeth prophecies. It was his decision to do so after Lady Macbeth persuaded him. Although the witches' intentions was probably to cause this murder, the witches did not make Macbeth muder Duncan.
she talked him into killing the King by accusing Macbeth of being weak and cowardly
The crucial part. Without Lady Macbeth, this would have been Macbeth's final decision: "We will proceed no further in this business." Macbeth would never have killed Duncan unless Lady Macbeth had goaded him into it.
Naming his useless son Malcolm as his heir instead of the able and well-respected Macbeth was a foolish and selfish decision.
Duncan's decision to name his son, Malcolm, as his heir instead of Macbeth, and his decision to stay at Macbeth's castle without informing him both upset Macbeth.
She tells him that he has to die so MacBeth can become king.
Lady Macbeth persuades Macbeth to follow through with the plan to murder Duncan. She calls him a coward and less than a man, prodding Macbeth to follow her plan. Macbeth agrees to murder Duncan that night.
Macbeth tells Lady Macbeth that he has decided not to go through with the plan to kill King Duncan.
Macbeth's decision to kill Macduff's family causes Macduff to seek revenge, leading to Macbeth's downfall. If Macbeth had chosen differently and not committed this act of violence, Macduff may not have been as determined to bring about Macbeth's demise, potentially altering the course of events.
The witches only gave Macbeth prophecies. It was his decision to do so after Lady Macbeth persuaded him. Although the witches' intentions was probably to cause this murder, the witches did not make Macbeth muder Duncan.
MacBeth was King of Scotland from 1040-1057 and was nothing like the Shakespeare MacBeth.
Scotland
she talked him into killing the King by accusing Macbeth of being weak and cowardly
He kills the chairman, and he admits it saying he did it out of rage, scaring Duncan's sons more.
The crucial part. Without Lady Macbeth, this would have been Macbeth's final decision: "We will proceed no further in this business." Macbeth would never have killed Duncan unless Lady Macbeth had goaded him into it.
Macbeth :)