Final answer:
In Act Three of Macbeth, his leadership is questioned due to his tyrannical rule, exemplified by his brutal actions and the fear he instills in others, leading to a rebellion against his authority.
Step-by-step explanation:
During Act Three, Macbeth's leadership is called into question due to his tyrannical rule. Instances in the play illustrate his harsh and cruel behavior towards others, and his wielding of power in a manner that breeds fear and dissent. Rather than displaying cowardice, indecision, or a lack of ambition, Macbeth's actions and the reactions of those around him suggest a growing dread and disapproval of his despotic actions, exemplified by the fear of the nobleman who turn against him and the dissatisfaction that leads to eventual upheaval.