It is possible to argue that the feudal system proves Hobbes's view of human nature because people in that system tended to act in accordance with their selfish interests. In the feudal system (as opposed to in an absolute monarchy) the various important lords had the ability to act in their own interests in ways that may well have been harmful to the state as a whole. This would tend to support Hobbes's idea that an absolute ruler was needed in order to check the selfish impulses of the people.
The history of feudal Europe is littered with examples of people acting in very selfish ways. Members of the nobility were constantly fighting to advance their political interests. They would often do this even if it meant that their country as a whole would be harmed. As an example of this, we have events like the one in which Eleanor of Aquitaine led a revolt against her own husband, King Henry II of England. This sort of behavior by people in feudal times seems to confirm Hobbes's views of human nature.