
In West Side Story, two rival gangs, Jets (American) and Sharks (Puerto Rican) are in a dead heat battle. Long story short, Tony who is a Jet, falls in love with the Shark's leader's sister, Maria and the huge controversy ends in Tony killing the shark leader Bernardo, and Tony gets gunned down by Bernaro's friend chino.
West Side Story relates to Romeo and Juliet mainly because of the forbidden love factor. In both pieces of work, there are two enemy families who disapprove on mixed relations between themselves. I see West Side Story as a modern and moderately altered version of Romeo and Juliet because of its qualities embedded into the plot.