Question: why are norway and denmark fight in hamlet?
Answer: After the Ghost vanishes, Horatio explains that King Hamlet (Prince Hamlet's father) had slain King Fortinbras of Norway in combat and reclaimed land for Denmark. He adds that young Fortinbras "Of unimproved mettle hot and full" (1.1. 96) is massing an army to win back the land that King Hamlet had taken.