Although the movie Westside story and the play Romeo and Juliet had the same theme; there are many different principles that led to the different endings. Since the movie Westside story took place in present time New York. The level of civility, the amount of individual freedom, the laws, the loyalty and friendship between the people made a big difference in how the story was performed and how it ended.
In the movie Westside story the party was planned by the owner of the gym. Both gangs the Sharks and the Jets came to the party. In the play written by William Shakespeare, the Capulets planned the party and only three people from the Montague's family came. This difference has a lot to do with how civilized different groups of people are. When a city becomes more civilized over time the citizens in their city must peacefully coexist with other people. Since the society was more stratified years ago only the invited relative or friends could come to a party. .
In the play Romeo and Juliet, Romeo had to run away in order to meet Juliet. In the movie Tony walks to the place where Maria lives freely. This difference is caused by the individual freedom of the people who lives in a city. Some time ago many young people didn't have a lot of individual freedom so they were mostly locked away in the house of their family. Since the movie took place in present time New York, people were given more freedom. Consequently Tony doesn't run away to meet with Maria instead he walks confidently to Maria's house.
Instead of fighting on the street as in the play Romeo and Juliet, the two gangs plan, a rumble without weapons. The law that the citizens have to follow today, such as no fighting or killing causes this variation from the play. Due to this law the two gang leaders, Benardo and Riff had to plan a secret fight in order to avoid the consequences of disobeying the law.