At the beggining of the act IV Hamlet had already killed Polonius and because Hamlet is a beloved prince among the people of Denmark, King Claudius couldn´t be severe on his punishment he decided to send Hamlet to England which had fall into the control of the king´s empire. In secret Claudius wrote a letter to the king of England ordering him to kill Hamlet when he arrives. The king sent Rosencrantz and Guildenstern to scort him to the ship that would carry him to England.
When they were going they crossed with a captain from Fortinbras´s army that was going to ask for the King´s permission to travel through his lands in order to get to Poland and attacked them for a territory in dispute between the kingdoms of Poland and Norway. Hamlet asked the captain what was the basis of the conflict and the captain replied to him that they were going to war for a "a little patch of land" with no profit more than the honor.
Hamlet was astonished by the thought of a bloody war could be fighted for something so insignificant. He compared the attitude of Fortinbras with his own and felt disgusted because he had a great deal towards Claudius and yet he delayed and failed on his purpose several times. Finally he declared that from that moment on he was going to focus on his revenge and how to made it possible.
This is an excerpt in which he declares this final intention:
"Oh, from this time forth,
My thoughts be bloody, or be nothing worth!" act 4, scene 4.
I hope the answer help you. Regards.
