Grendel and the dragon wage war for different reasons. what are these reasons? how are these different motivations related to underlying themes of the epic?

Grendel wages war, that is terrorizes Heorot and its inhabitants, because he is a carnivorous, devilish creature that is committed to disturbing the king's peace and prosperity of the realm. The Dragon, on the other hand, wages war simply because a slave stole a cup from the treasure he had guarded for ages. So, his motivation is retribution. Grendel is a subverted human, the descendant of Cain, so he challenges the king and his subjects. The Dragon is something less particular, a kind of irrational force that subverts the order itself. He strikes Beowulf's kingdom. The clash of the two of them will end with both being dead, and the conflict unresolved.