Shakespeare's famous play Romeo and Juliet stems from both a true account of history and a legend. It is known that dating all the way back to the 12th century and persisting into the 14th century, two factions of warring families arose in Verona. The families are known as the Guelphs and the Ghibellines. The Guelphs were wealthy merchants who supported the reign of the Pope, while the Ghibelline were a family of dukes who felt that the Holy Roman Emperor would best protect their land, wealth, and interests. The Guelphs also became known as the Montecchi, or Montagues, while the Ghibellines became known as the Cappellini, or Capulets, as we know from several historical sources, and Dante even mentions them in The Divine Comedy. Thus, these are the two warring families that Shakespeare depicts in Romeo and Juliet.
However, the story of the wealthy, star-crossed lovers also stems from a historical legend. Vicenza Luigi da Porto wrote a historical account he called what can be translated as "The history of two noble lovers and their piteous death occurred during the reign of Bartolomeo della Scala" ("Verona: The history," veronafor2.com). This is the work from which Shakespeare obtained his plot and most of his characters, especially Romeo and Juliet. We also believe that the story existed as an oral account long before da Porto put it in writing.
Hence, we know that the two family factions Shakespeare depicted existed and we know that a legend of two star-crossed lovers who were members of these families existed. However, we don't know for sure how much the legend is based on historical fact.
In my personal interpretation, one who writes well and is highly recognized for it is one who has written about their life or something they strongly believe in because the events in their life. Shakespere wrote about a Romero and a Juliet because in his life a Romeo and a Juliet did exist and were real people.
“It’s an illusion that writers have a lot of choice about what they write,” she explains. “Your stories are your stories. They’re the only ones you can really tell, and if you try telling ones the world would like you tell, you’ll do it badly.” – Curve Magazine 2001