The final scene of Romeo and Juliet is triumphant because the "ancient grudge" (Prologue) has finally been resolved.
In the last scene of Shakespeare's tragedy of two warring households, the Prince calls together the Capulets and the Montagues and chastises them:
Where be these enemies?—Capulet! Montague!See what a scourge is laid upon your hate,That heaven finds means to kill your joys with love! (5.3.307-309)
...raise her statue in pure gold;
That while Verona by that name is known,
There shall no figure at such rate be set
As that of true and faithful Juliet. (5.3.314-317)
After Romeo and Juliet die, it makes both Capulet and Montague relize that there fighting is pointless... they both lost the ones they love due to some old family rivalry. This makes them relize that there was no point in fighting and so they both become "friends" after the huge fued. For example, they both build statues of each families lost one ( made in gold)