romeo because romeo loves juliet.
Nothing, really. Romeo reacts to Tybalt's actions on his own volition. Because he doesn't want to see his cousin and his friend fighting he tries to break up the fight. Because Tybalt killed Mercutio, Romeo wanted revenge on Tybalt. But Tybalt didn't make Romeo seek revenge; Romeo could have walked away from it all, and watched Tybalt be executed for his crime while he gets to spend the rest of his life with Juliet.
Juliet's cousin's name was Tybalt. Tybalt murdered Romoe's best friend, Mercutio, so Romeo killed Tybalt in revenge.
At first, Romeo does not want to fight with Tybalt because he is now married to his kinswoman, Juliet. This makes Romeo and Tybalt of the same family, and Romeo does not want to fight his own.
Tybalt
romeo went to find Tybalt not Tybalt to find romeo after Mercutios death to get revenge
Mercutio is killed by Tybalt in a fight, and Tybalt is subsequently killed by Romeo in revenge.
Mercutio and Tybalt were having a brawl, when Tybalt actually thrust his sword into mercutio, causing him to die. Romeo gets revenge for Mercutio, and dukes it out with Tybalt until he finally killed him.
Tybalt is Juliet's hot-headed cousin. He kills Romeo's best friend, Mercutio, in a feud. Romeo, angry and wanting revenge, kills Tybalt.
Tybalt's uncle, Lord Capulet, is furious when Tybalt is killed in a fight with Romeo. He seeks revenge and demands that Romeo be punished for Tybalt's death. His anger and grief lead to escalated tensions in the play.
Tybalt sent the challenge because he was angry that Romeo came to the party and that Capulet scolded Tybalt for not enduring Romeo. Tybalt was embarrassed by this and wanted revenge
Romeo kills Tybalt (Juliets cousin, a Capulet) to revenge Mercutio's death, as Tybalt stabbed him. Mercutio was a Montague and jumped in the way of Tybalts sword to defend Romeo, who wanted peace from Tybalt as he had already secretly married Juliet. Romeo is then banished by the prince and the rest of the play goes on. Basically, Romeo kills Tybalt for revenge.
Tybalt has vowed revenge upon Romeo and has sent a challenge to Romeo's father's house.