What theme did Tybalt contribute to in Romeo and Juliet? How would the story be different if he were not written in?

In the play, Romeo and Juliet, Tybalt's character contributes to the theme of hatred which breeds disaster. From the moment we first meet him in Act 1, scene 1, he is displaying his great enmity for the Montagues and challenging Benvolio to fight with him.

Tybalt:

What, art thou drawn among these heartless hinds?

Turn thee Benvolio! look upon thy death.

Benvolio:

I do but keep the peace. Put up thy sword,

Or manage it...

In the play, Romeo and Juliet, Tybalt's character contributes to the theme of hatred which breeds disaster. From the moment we first meet him in Act 1, scene 1, he is displaying his great enmity for the Montagues and challenging Benvolio to fight with him.

Tybalt:

What, art thou drawn among these heartless hinds?

Turn thee Benvolio! look upon thy death.

Benvolio:

I do but keep the peace. Put up thy sword,

Or manage it to part these men with me.

Tybalt:

What, drawn and talk of peace? I hate the word

As I hate Hell, all Montagues , and thee!

Have at thee, coward!  (lines 64-70)

Then, in Act 1, scene 5, Tybalt overhears the voice of Romeo Montague at the Capulet Ball. He immediately becomes enraged at this affront to his family's honor and asks for his sword but is stopped by Lord Capulet, who does not wish to have any unpleasantness mar his party, especially in front of his guests.

Finally, in Act 3, scene 1, Tybalt's festering hatred for Romeo reaches its bitterest and most violent point as he challenges him to a fight, in order to defend his family's honor. Romeo, who has secretly wed Juliet and is therefore now Tybalt's cousin through marriage, feels love for Tybalt and refuses to fight him. Mercutio steps in and insults Tybalt; they fight and Mercutio is slain by Tybalt's sword. Romeo now views Tybalt as a villain and fights him to avenge the death of his best friend.

Although Tybalt is killed by Romeo, it is his avowed hatred, hubris and impulsivity that contribute to his own disaster, as well as to the ultimate fate of the star-crossed lovers. The character of Tybalt is, therefore, the embodiment of the theme that hatred breeds disaster.