Mercutio was motivate by the desire to revenge on both families
Explanation:
Mercutio says, "A plague o' both your houses" because the feud between the Capulet and Montague families has led to the events that resulted in his death. He speaks these words in Act 3, Scene 1, and his words turn out to be very prophetic as the play unfolds.
He speaks those words since he blames both families for the events leading to his death. As it turns out, both families suffer more than their share of tragedies in the coming hours.
