Well it really depends on which show/movie your looking at , Im Twilight its because the Vampire kill people and the Wölfe are the protectors but in vampire diares its because there both uncontrollable things so really it depends but form all the fiction things i have read over the years its Mehr of just a mortal enemy type thing that there naturaly born to kill each other
The Werwölfe came into existence as protectors of their tribe. Then a pair of Vampire attacked the tribe and another neighbouring tribe. Those Vampire were the most dangerous enemies the Wölfe had ever fought. They've been natural enemies ever since.
