Macbeth is the only character in the Shakespearean tragedies who qualifies both as a hero and a villainy. As the play develops his heroism gives way to villainy. Probably this is because of the conflict in his character( both internal and external). This results in the downfall of Macbeth. The external conflict is mainly from two areas: Lady Macbeth and Witches. The internal is because of his vaulting ambition.
In the beginning of the play Macbeth is considered as a kind soldier. This "too full o' the milk of human kindness" is a problem for Lady Macbeth. Because this kindness does not allow Macbeth to kill Duncan. She wants Macbeth to overcome this kindness to become the king of Scotland. Hence she instigate Macbeth to make a plan to kill Duncan. This may be the major external conflict which Macbeth faces. Because of this conflict he kills Duncan and latter on commits a train of murder.
May be the first source of conflict is because of the interference of three witches. They are the one who planted the seed of ambition in his mind . They greet Macbeth, " All hail , Macbeth, that thou shall be king hereafter". This indeed a great source of conflict for Macbeth. Soon afterwords Banquo notices it too and tells, "Good sir, why do you start: and seen to fear/ Things that do sound so fair?" I' the name to truth/ Are ye fantastical.
His conflict did not come to an end even after killing Duncan. It increased more afterwords. He did not realise that the throne of Scotland would not provide him with no peace.From then onwards he becomes a senseless murderer, as he first kills Banquo and later Lady Macduff and her son.This in fact is the major cause for the down fall of Macbeth.