Answer:
Basically, in Act 2, Romeo and Juliet are married by Friar Lawrence, in hopes of uniting the two factions. Romeo kills Tybalt(Capulet) (he killed his friend, Mercutio, a Montague) and now Romeo is banished. The Nurse and Juliet freak about this for a while, and Juliet is told by her father she is to marry a man named Paris despite being secretly married. Friar Lawrence gives Juliet a potion so she will go into a coma and appear dead so she can run off with Romeo. No one tells Romeo this. Romeo thinks she's really dead and kills himself. Juliet wakes up, finds out Romeo is dead, and kills HERSELF. This, weirdly, ends the Capulet's feud because they both realize they lost two kids to their irrational disagreement. This is forshadowed in the play's prologue when they say "From forth the fatal loins of these two foes. A pair of star-cross'd lovers take their life; Whose misadventured piteous overthrows. Do with their death bury their parents' strife." (Shakespeare). Act 2 ends with this age old conflict being rectified and the two factions are now friends.