In Romeo and Juliet, what does Prince say is the history of the feud and what will be the consquences of the future feuds?
After the street fight in the beginning of Romeo and Juliet, Prince Escalus appears with his attendants. Angered that no one at first hears him, he calls them "Rebellious subjects, enemies to peace" (I,i,54). Stating that this brawl is the third of those between the Montagues and the Capulets that have disturbed the peace of Verona, the Prince tells the old enemies,
If ever you disturb our streets again,/Your lives shall pay the forfeit of the peace. (I,i,70)
That is, the Montagues and the Capulets cannot fight again or the Prince will have them killed.
Here in this speech of the Prince, the audience witnesses the juxtaposition of images that are in the Prologue; the Prince uses the same word play to make his point to the warring families: "Rebellious subjects," "men/beasts," "canker'd peace/canker'd hate."
This can be found in Act I, Scene 1, when the Prince comes in and sees the aftermath of the fight between the servants.
The Prince just says that the families have been feuding for a long time. He does not say why they do not like each other. We never do find that out. He says that they have fought out in the public streets three times, just because of comments that have been made (this appears to be just in recent times).
The Prince says that anyone fighting in public again will be subject to the death penalty. His exact words are:
If ever you disturb our streets again,
Your lives shall pay the forfeit of the peace.