How does Shakespeare use foreshadowing in the prologue to 'Romeo and Juliet'?

The prologue to Romeo and Juliet tells us precisely what will come in the play that is to follow. We are informed that the story will involve two families - "two households" - who are equals in their position in society, but are enemies. Their "ancient grudge" will have catastrophic affects on the younger, innocent generation, as indicated in lines 3 and 4: "... break new mutiny / Where civil blood makes civil hands unclean". This shows the lack of reason for the grudge between the two families: there is no need for the fighting, these are "civil" people, good people, who will be ruined by this ancient war. The children of these two families will fall in love and end up killing themselves, and this is hinted to be as a result of the meaningless grudge between the two families. Shakespeare was not ruining the plot in having the chorus outline the plot in this manner, as the story of Romeo and Juliet was already well-known - the majority of the audience attending would already have been aware of what was going to happen in the play. The intrigue in the play lay in how this story would unfold upon the stage, as Shakespeare wrote: "the continuance of their parents' rage, / ... Is now the two hours' traffic of our stage". He implies the audience to watch attentively to the nuances of the story as it unfolds, relying not upon the shock of the ending but the intricacies of the characters' stories.