How does William Shakespeare create tension throughout Act 3 Scene 1?

From the minute the play starts the audience are aware that the "star crossed lovers" Romeo and Juliet are going to die, this makes it clear that the play is a tragedy. A Tragedy is a traditional form of theatre where the main characters in the play die as a result of their tragic flaw, for example in the tragedy play Macbeth, Macbeth's vaulting ambition leads him to his death. Romeo and Juliet's flaw is …

…for the Capulet Family. Although if Mercutio had known about Romeo and Juliet his anger would not be so great. I found the play sad because two innocent characters had to die because of their flaw which was the powerful love between them which could not be broken and I also feel that another reason Romeo and Juliet died was the feud between the two families which was ended only when there children had died.