What is the social and historical context of "Romeo and Juliet"?
What was life like in Shakespeare's time, and how might it have influenced the play? Where is the play set, and why did Shakespeare set it there?
The play is set in Verona, Italy, during the Renaissance. The story of two warring noble families would not have been unfamiliar to Elizabethan audiences, who, by 1597, when the play was written, would have been familiar with the feud between the Stuarts (e.g., Mary, Queen of Scots) and the Tudors (e.g., Elizabeth I).
The Capulets and the Montagues are described by the chorus as "two households, both alike in dignity," but mired in an "ancient grudge" that broke out into "new mutiny." The "strife" between the families was only broken by the tragic deaths of their children, "star-crossed lovers."
In Italy, at the time at which the play was set, a few noble families had risen to great political and economic power and prestige during the Renaissance, most notoriously the Medicis and the Borgias. The Medici family was a banking family and political dynasty that later became a royal house—just as the Montague and Capulet houses are noble houses.
Both families were involved in scandals and intrigues, including assassination attempts. The Borgias had a more venal reputation, but there is a possibility that certain members of an Elizabethan audience would have known something about these families. Even if they did not, they understood the drama of political intrigue and had learned about similar rivalries for power within their own country.
This is a huge question, to which whole books have been devoted, so can only ever be briefly answered in this context: I'll focus my answer on context specifically helpful for "Romeo and Juliet".
The Elizabethan society was strongly patriarchal, and a father had the right to treat his daughter as saleable goods (have a look at Capulet's treatment of Juliet in 4.). Marriage was a business agreement, and one of the reasons Capulet is so keen to marry Juliet off to Paris is because it represents a sound business investment.
The 'plague' which Mercutio prophesies with his dying breath, and which eventually stops Friar John from delivering the fateful letter which leads to the lovers' suicide was also a far more terrifying prospect than a 'plague' in modern day. The Black Death - the bubonic plague - was continually recurring in Europe between its first outbreaks in the 14th century and the 18th century: and outbreaks of disease regularly killed huge percentages of the population. Thus the equation Shakespeare makes between violence and disease was one which had its basis in a very real contemporary fear.
The play is set in Verona, an Italian city traditionally associated with hot-bloodedness and passion, and one which Shakespeare probably never visited. But the play's setting points to the Elizabethan obsession with Renaissance Italy - considered the height of fashion, particularly where young lovers were concerned.