What are two quotes from Romeo and Juliet that help analyze how the feud between the Montagues and Capulets lead to the deaths of Romeo and Juliet?

Here the Montague's and the Capulets reflect the constant tension between the two families.

ABRAHAM
Do you bite your thumb at us, sir?

SAMPSON
I do bite my thumb, sir.

ABRAHAM
Do you bite your thumb at us, sir?

SAMPSON
[Aside to GREGORY] Is the law of our side, if I say
ay?

Here Tybalt shows his hate for Romeo (Tybalt doesn't actually know Romeo) at the Capulet Party.

This, by his voice, should be a Montague.
Fetch me my rapier, boy. What dares the slave
Come hither, cover'd with an antic face,
To fleer and scorn at our solemnity?