I think this is most clearly shown in Mercutio's famous line 'a plague a' both your houses'. This is possibly the biggest insult that he could have said to either of them, but he takes no caution in saying it, as he is on his deathbed. Raw passion for their house is seen virtually in every scene, such as what we see in Act 1 scene 5, when Tybalt is furious with the Romeo's presence at the party at the Capulet house, and is positive he must leave. It is only when he is forced by Capulet to ignore his presence that he does so. Even then he is determined to get revenge. He says: 'but this intrusion shall, Now seeming sweet, convert to bitterest gall.' This seems to put a black feeling on to the meeting of Romeo and Juliet which happens as soon as he has spoken.
It is shown that characters feel so strongly about conflict and protecting their family honour because they believe it is their destiny. We see throughout the play that astrology and fate means a lot to the characters, as it did to most people at the time. Romeo and Juliet are described in the prologue as 'Star-crossed lovers', something that turned out to certainly have elements of truth in it. These were two people who paid the ultimate price of death, just because it wasn't their destiny to be together.
Throughout the entire play we see what conflict is and how it can occur, but in the end, at least some of the characters realize that all of their loyalty was worth nothing. After Romeo and Juliet's deaths, their fathers agree to drop the feud. But conflict has resulted in a number of avoidable deaths and Shakespeare seems to be saying that it is in the end wasteful and tragic that mindless conflict can do such damage. In the historical poems, 'Dulce et Decorum Est' and 'The Charge of the Light Brigade' we are given a good idea of how two writers can have different opinions about war and conflict. In 'Dulce et Decorum est' the first line is 'Bent double, like old beggars under sacks' suggesting war ages men before their time.