The play "Romeo and Juliet" by William Shakespeare never mentions why the Capulets and Montagues are fighting. The only thing that is clear is that it is a long-standing family feud that comes up numerous times in the play, including in the opening scene.
From the first scene of "Romeo and Juliet," in which the servants of both families scuffle, Shakespeare makes the bitter rivalry between the two families an essential part of the plot. According to the Royal Shakespeare Company of Great Britain, the violence in the Capulet-Montague feud exemplifies the violence throughout the city of Verona. From young to old, violence motivates the deeds of many of the supporting characters. The only way to assuage it is by the death of the two lovers at the end of the play. At that time, the two families see the folly of their rivalry, and Friar Lawrence is finally able to persuade them to set aside their grievances and reconcile.
Romeo is of the house of Montague. Romeo's parents are not presented with characters as harsh as those of Juliet. His mother dies of grief when he is banished. Juliet is of the Capulet family. Her father is domineering and subject to fits of rage, and her mother is intensely vindictive and at one point threatens to kill Romeo. Juliet can only look to her parents for discipline, never for sympathy. The Royal Shakespeare company points out that this violence in the hearts of the parents masquerades as love and compels the conclusion of the play.