Which events in Act 1 seem key to setting up conflicts that will move the action of the rest the play forward?

Act I, begins with a fight between the Capulet and Montague servants..... something that sets the tone for the rest of the play. Quickly after the servants commence fighting, Benvolio (Romeo's cousin) and Tybalt (Juliet's cousin) join the fray. In Scene IV, Romeo and the rest crash the Capulet party..... Romeo falls in love with the one girl he cannot have, and the rest is history. These two families cannot call a truce, and the younger members of the family act impulsively, without thought.