Well the question is how did he do this, how did he build up the tension? As we see throughout the play there is a lot of dramatic irony used which means the audience know what is happening but the characters do not. This causes the audience to become intense and think what is going to happen next. For example when the fighting scenes begin and there is a conflict between Benvolio, Romeo, Tybalt and Mercutio, at that time the audience realize at the beginning of the play there was a conflict as well and it ended up in a big fight and the prince addressed that anyone who fought from the Montague and Capulet families would get sentenced to death. There fore this brings tension within the audience thinking, will there be a fight? Who is the victim? Oh no! Romeo shouldn’t get into this.
Suddenly Mercutio is murdered by his own family member which would surprise the audience and make them think why that had happened and the Mercutio right before dying he shouted three consecutive times plague to both your families, and the audience at that time beloved in cursing and that time was the time of the plague, there for this builds up tension and makes the audience think do they really want to be in an auditorium with people inside it with plague? This is how Shakespeare builds up the tension at the beginning within the audience. And this is were he added to the tension, the audience realized that now Mercutio is dead and the hot tempered Tybalt will be sentenced to death, this has already built up tension allowing them to think what is going to happen next in the story.
But then they realize at the beginning it was mentioned that the two lovers will not meet again, and meanwhile Romeo wants to fight against Tybalt for the death of his friend Mercutio so here the audience realize if Romeo kills Tybalt the lovers will never be with each other, and Romeo does not realize that while being very angry for Tybalt’s actions, this causes a dramatic irony in the story, it is where the people realize something bad is going to occur in the story but the characters do not realize that. And it was only a while ago where Romeo had married Juliet, there for no one there knows about their marriage but him and the audience this also builds up tension because he then is fighting his own relative and this is not only bad because he will get a death sentence but it occurs to the audience that this will make Juliet not like her husband for slaughtering her cousin. It is strange how yet still nowadays which is 100s of years after Shakespeare we get the tension; this is from the cleverness of Shakespeare, which grasped everybody’s attention to his plays.