I would argue there are several tragedies in Macbeth. I'll discuss a few for you. First is the natural tragedy of man and greed. The tragedy arrives from Macbeth's own inner weakness in believing the witches for their prophecies and then being manipulated by his wife to act out and expedite said prophecies. Yet, you may want to jump and say, "But his wife made him..." while this is true, keep in mind when he hears the witches' prophecy the idea of killing the king does cross his mind, therefore the seed is planted. Another tragedy is suffered by Macduff. By choosing to be suspicious of Macbeth and pose as a threat (whether he was aware of it or not) his house is slaughtered at the hands of hired murderers, sent by Macbeth. His young son and wife are both killed, causing him great grief and subsequently being the "straw that broke the camels back" and sealing Macbeth's fate. A final tragedy, if you want to do some speculating and include gender studies, is the impact the loss of a child has on a mother. Some scholars and educators propose that Lady Macbeth and her husband lost a child prior to the opening of the play (See "MACBETH" 2006 indie film from Australia... portrays an excellent interpretation of this in the opening scene). Through this tragic loss, Lady Macbeth because callus and maliciously motivated.
Macbeth is a tragedy because a relatively good man who has the qualities to become a great man is derailed by his greed and lust for power.The prophecies of the witches begin his journey down the path of destruction. He could have ignored them, as Banquo did, and allowed fate take its course. Instead, with the encouragement of his wife, he takes matters into his own hands, murders his king and from then on his ambition overtakes him. He lets nothing or no one get in the way of his success.He has chances to reverse his course, but his ambition is too strong. By the time the play is over, his wife has gone mad and killed herself, Macbeth has had Banquo killed, along with his wife and young son, and Scotland is in disarray. Believing his will not be killed by "a man born of a woman" he is killed nevertheless by a man born by Caesarian section. He has lost everything, including his kingdom and his reputation.