In the prologue of Romeo and Juliet, a longstanding, violent feud between two families is introduced:
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.
As the play begins, we learn that the feud is between the Montague (Romeo’s family) and the Capulet (Juliet’s family) families. With the word “ancient” mentioned in the prologue, we can assume that this feud has been going on for generations. In fact, both the younger and older generation continue to feud publicly, forcing the Prince to issue a decree of banishment for more disruptions of peace.
The consequences of this feud impact Romeo and Juliet’s relationship. Heartbroken, Romeo is convinced by his friends to crash the Capulet ball. Upon laying eyes on Juliet, he is smitten with her (Act I, Scene V):
Did my heart love till now? Forswear it, sight,
For I ne’er saw true beauty till this night.
When Romeo and Juliet figure out that they are from feuding families, Romeo continues to pursue her while Juliet thinks through the consequences of relationship a bit more carefully, considering their families’ histories. In the end, they decide to pursue marriage.
Early in the morning, Romeo visits the Friar to ask him to marry them. The Friar is understandably shocked because just moments ago, Romeo was “in love” with Rosaline (Act II, Scene II):
Holy Saint Francis, what a change is here!
Is Rosaline, whom thou didst love so dear,
So soon forsaken?
While the Friar doesn’t believe that Romeo is truly in love with Juliet, he begins to meddle in their relationship and the feud, agreeing to marry them, for the sole purpose of ending the feud between the families (Act II, Scene III):
But come, young waverer, come, go with me.
In one respect I’ll thy assistant be,
For this alliance may so happy prove
To turn your households’ rancor to pure love.
In a tragic way, the Friar is successful in his original purpose for the marriage. While Romeo and Juliet both die (among others), their deaths allow the Montagues and the Capulets to seek peace so that more innocent lives will not be taken.