Through the murders of Duncan and Banquo Macbeth begins a civil war that consumes Scotland and ultimately leads to his downfall as an army marches on Dunsinane and secures the throne for Malcolm. In a more personal sense, however, his actions bring about the destruction of his marriage, as Lady Macbeth loses her wits in the face of crushing guilt. His wife, with whom he once shared what seems to be a very loving relationship, kills herself as Macbeth prepares to face the rebel army. Perhaps more directly, Macbeth's decision to have Macduff's family murdered (he wanted Macduff murdered, as well, but he was not there when the assassins arrived) makes an implacable enemy for him. This fulfills the prophecy of the witches, who have summoned an apparition that tells Macbeth he cannot die except by the hand of a man "not of woman born." Just before he kills Macbeth, the vengeful Macduff informs him:
Despair thy charm,
And let the angel whom thou still hast served
Tell thee, Macduff was from his mother's womb
In other words, Macduff was born by Caesarian section, and was fated to kill Macbeth. It is, of course, debatable whether the supernatural or human agency is the more powerful force in the play. But it was clearly the "evil deeds" of Macbeth, particularly his murder of Macduff's family, that brought the two men to their encounter on the battlefield.
Macbeth commits a series of murders throughout the play that lead to his downfall. As was mentioned in the previous post, Macbeth's downfall begins when he commits regicide by killing King Duncan. After killing Duncan, Macbeth realizes that his position as king is threatened. He knows from the witches' prophecy that Banquo's descendants will be kings. Macbeth then orders assassins to murder Banquo and his son, Fleance. The assassins successfully kill Banquo, but Fleance escapes. Macbeth begins to feel extremely guilty after Banquo's death and begins to see Banquo's ghost during a feast. Macbeth then has Lady Macduff and her son killed. By the end of the play, Macbeth turns into a callous tyrant who is only concerned with protecting his position as king. Macbeth's unchecked ambition and bloodlust led to his downfall.