In grendel by john gardner, why was the twelve-year war a misunderstanding?

Basically, Grendel is a novel by John Gardner that retells the part of the Old English poen Beowulf from the perpective of the antagonist. This novel deals with finding meaning in the world, the power of literature, myth and the nature of the good and evil. It is a misunderstanding hence Grendel in the novel, he portrayed as an antihero. Thus, Grendel can understand the humans but humans cannot understand him and they become frightened which leads to a fight between Grendel and the Danish warriors. It was just that Grendel was saved from death at the hands of the humans by the appearance of his mother. 

what is the sentence?

the answer is "began" because it is a action that can be done