“If ever you disturb our streets again, your lives shall pay the forfeit of the peace.”
Prince Escalus wants peace. He does not want the Montagues and Capulets fighting any more. Therefore, any quote that speaks of actually fighting should be immediately dismissed: "Draw if you be men!" AND "Strike! Beat them down! Down with the Capulets! Down with the Montagues!" Tybalt is the one who says, "What, drawn and talk of peace? I hate the word, as I hate hell, all Montagues, and thee." This line is one of the most quoted lines of Tybalt in the entire play. It's worth remembering.
In his warning Prince Escalus tells the Montagues and Capulets that if they fight again that the consequence will be death. When Tybalt kills Mercutio and Romeo kills Tybalt, the Capulets ask for Romeo's head. They argue that the Prince said the consequence would be death. However, the Prince decides to only issue a consequence of banishment since both Mercutio and Tybalt died.