The theme of family feud in Romeo and Juliet is central to the tragedy and drives the plot forward. The "ancient grudge" between the Capulets and Montagues creates a backdrop of conflict that affects not only the two families but the entire city of Verona. This longstanding animosity forbids Romeo and Juliet from openly expressing their love, ultimately leading to their tragic demise. The feud is depicted as senseless and destructive, highlighting the futility of such deep-seated hatred.

The opening scene of the play immediately establishes the depth of the feud. It reveals that the conflict is not limited to the family members but extends to their servants and the wider community. The servants of the Capulet household, Sampson and Gregory, express their readiness to fight simply because their masters are at odds. This indicates how the feud has permeated every level of society. Prince Escalus's speech further emphasizes the extent of the feud's impact, noting that trivial remarks between the families have led to "three civil brawls" that disturb the peace of Verona:

Three civil brawls, bred of an airy word
By thee, old Capulet, and Montague,
Have thrice disturb'd the quiet of our streets. (I.i.85-87)

Juliet's reflection on the feud underscores its irrational nature. She muses that it is merely Romeo's name that is her enemy, suggesting that the feud is based on superficial distinctions rather than substantial grievances. Her famous line, "'Tis but thy name that is my enemy," reveals her belief that their love should transcend the feud. However, this underestimation of the feud's power proves fatal, as the lovers' attempts to defy their families' enmity lead to their deaths.

The feud also serves to heighten the contrast between love and hate. Romeo and Juliet's love is portrayed as pure and intense, yet it is constantly threatened by the surrounding hatred. The destructive nature of the feud amplifies the stakes of their relationship, making their love appear even more passionate and desperate. The senselessness of the feud is further highlighted by the fact that its origins are never fully explained, suggesting that it persists out of habit rather than necessity.