What does the young prince Fortinbras want to do in the play, Hamlet?
In Act l, Scene 1, Marcellus, who is keeping watch with others on a platform outside the castle Elsinore, asks Horatio the reason for their vigilance. Horatio replies, in part:
Now, sir, young Fortinbras,
Of unimproved mettle hot and full,
Hath in the skirts of Norway here and there
Shark'd up a list of lawless resolutes,
For food and diet, to some enterprise
That hath a stomach in't; which is no other--
As it doth well appear unto our state--
But to recover of us, by strong hand
And terms compulsatory, those foresaid lands
So by his father lost:
The lands that Horatio refers to seem to be property that the deceased king Hamlet had won from the erstwhile king Fortinbras of Norway, whom he had killed in battle. In terms of his victory, all land previously won by the deceased Fortinbras became the victor's spoils in terms of a sealed agreement which was ratified by law and custom.
It appears that the young Fortinbras, son of the slain Norwegian king, had raised an army of mercenaries with whom he now intends to reclaim these lost properties by violent means, i.e. through war against Denmark.
This fact is later verified in Scene 2 by king Claudius, Hamlet's uncle and stepfather and the usurper of the Danish throne, when he explains the purpose of young prince Fortinbras to his two emissaries, Cornelius and Voltimand.
Claudius states that the young prince had repeatedly written letters to Denmark demanding the surrender of his father's property, to which he was entitled. Fortinbras seemingly believed that the state of Denmark was in disarray and in a weakened state after the king's untimely death and that he could, therefore, demand redress.
Claudius is sending his two emissaries to Norway to deliver letters regarding the matter to prince Fortinbras's sickly uncle, the king of Norway, so that he may probably consult with his nephew and thus prevent an unnecessary war between the two countries.
Fortinbras later sends his captain to Claudius to seek permission to cross Danish soil in order to attack Poland. He will, therefore, not seek any redress from the Danes.
It is ironic that, at the end of the play, Hamlet leaves his title to the young prince which means that he would, as a rule, become king of Denmark, thus reclaiming his father's land through peaceful means. Before Hamlet succumbs, he tells Horatio:
But I do prophesy the election lights
On Fortinbras: he has my dying voice;
So tell him, with the occurrents, more and less,
Which have solicited. The rest is silence.
Prince Fortinbras is a foil to Hamlet. Although the two princes find themselves in similar circumstances in that their uncles are on thrones which they should occupy, the one is more fiery and determined (Fortinbras) whilst the other constantly ponders about his fate and what he has to do to avenge his father's murder.
We hear about young Fortinbras, a prince of Norway, in the very first scene of the play. In that scene, Horation, Marcellus and Bernardo have just seen the ghost and they are discussing what it might mean. They talk about some of the problems Denmark has been having and that makes them mention Fortinbras.
Hamlet (the dad) killed Fortinbras's dad. And now young Fortinbras wants revenge. He is invading Denmark. He wants to take back for Norway the lands that his father lost to Hamlet senior.
Fortinbras will be allowed to pass through Denmark to go fight in Poland. On his way back, at the end of the play, Hamlet will name him as the next king of Denmark.
Young Fortinbras has asked for permission to cross Denmark on his way to a military engagement with another country. The problem this presents for Denmark is that Hamlet’s father has killed Old Norway (Fortinbras’ father) in previous military engagement between the two countries. Another issue here is that Fortinbras is acting without the sanction of his king, who is also his uncle, as Claudius is to Hamlet. Hence, there is the possibility of revenge. Because Denmark is in a state of unrest over the death of Old Hamlet and Claudius’ succession, Fortinbras could easily intend to invade Denmark and stage a military coup.