Why is fortinbras perceived as a threat?

Fortinbras is perceived as a threat because he embodies ambition and military prowess, seeking to reclaim lands lost by his father, which signifies his desire for power and revenge. His determination to mobilize troops and assert control over Norway presents a direct challenge to the stability of Denmark, especially during a time of political uncertainty following King Hamlet's death. Additionally, Fortinbras's strong leadership and decisive actions contrast sharply with Hamlet's hesitation, highlighting the potential for disruption that Fortinbras represents. This makes him a figure of concern for Hamlet and the Danish court.