Tybalt, in his bloodthirsty hatred of the Montagues, played a critical role in instigating the sequence of events that led to the deaths of Romeo and Juliet. The critical scene is act 3, scene 1, when Tybalt, after challenging Romeo to a duel, kills Romeo's friend, Mercutio, instead. This act drives Romeo into a rage. The two fight, with Romeo killing Tybalt.
Already at this point in the play, Romeo and Juliet have been secretly married by Friar Laurence, but now Romeo is a criminal, facing banishment for the killing of Tybalt. Meanwhile, Juliet, in her grief, finds herself being pressured by her father to marry Paris (even threatened with disownment should she continue to refuse). Her desperation is so great at this point that she threatens to commit suicide should she be forced to marry Paris. It is in this context that Friar Laurence devises the plan to fake her death (a plan that later goes tragically awry).
In this context, Tybalt certainly holds a lot of responsibility for the deaths of...
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