Why does tony kill bernado in west side story?

Tony kills Bernardo in "West Side Story" out of a moment of rage and revenge. After Bernardo fatally stabs Tony's friend, Riff, during a confrontation between the Jets and the Sharks, Tony is overwhelmed by grief and anger. In a fit of emotion, he seeks retribution, leading to the tragic act of violence that escalates the conflict between the two gangs. This moment ultimately highlights the destructive cycle of violence and its devastating consequences.