Why does Macbeth have his friend Banquo murdered?

In the play "Macbeth", it is actually Macbeth, and not Banquo, who is the target of an attempted murder. It takes place on the evening of a banquet that Macbeth is hosting. During dinner, Macbeth has a mental breakdown, as the Ghost of Banquo, whom Macbeth ordered murdered earlier appears, seated in Macbeth's seat.