The want for revenge leads many of the characters in Romeo and Juliet into murderous acts which eventually leads to severe punishments and a further need for revenge. The everlasting revenge in Romeo and Juliet is first born from ancient grudge between the Capulets and the Montagues, which is ultimately settled with the tragic, abrupt unifying factor of both Romeo and Juliet's death. Several instances within the interactions of the characters suggests that vengeance is driving force of the plot, and that consequently, there must ultimately be an end to the feuding and recoil, due to the fact that there must be a resolution after the thrilling climax..
The first factor causing revenge springs from the ancient grudge between the Capulets and the Montagues, which curiously was never fully explained in the play. This ancient grudge is the initial justification that accounts for the two family's first dispute in the streets of Verona.
Two households, both alike in dignity,
In fair Verona, where we lay our scene,
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean. (Prologue)
However, after the first civil brawl, Romeo and Mercutio decide to intrude on the Capulet's masked party. Consequently, they eventually become discovered by Tybalt due to Romeo's easily distinguishable voice, yet Capulet discourages and scolds him from confronting Romeo and ruining the party. This humiliates Tybalt, and draws him into wanting to take the present matters into his own hands, dealing with Romeo and Mercutio some other time while his anger gradually builds.
This, by his voice, should be a Montague.
Fetch me my rapier, boy.
Am I the master here, or you? go to.
You'll not endure him! God shall mend my soul!...
Well said, my hearts! You are a princox; go:
Be quiet, or--More...