One theme in The Prince is human nature. Machiavelli has a rather bleak view of humanity in that he believes that it is dangerous for a prince to win the love of his subjects. It is also dangerous for a prince’s subjects to be perpetually afraid of him. Machiavelli believes that the prince needs to be perceived as just, whether he really is or not. He should be respected—that is the fine line between being loved and hated.
Another theme is military prowess. The prince should be an expert on the military and through this he will be able to ensure successful negotiations with other nations. Machiavelli believes that the prince's soldiers need to be homegrown so that they will fight for their own land instead of out of love for one's leader or love for money. At the end of the book, Machiavelli also argues for Italian nationalism and a united army. This is a unique thought because at that time Italy was a collection of feuding city-states.
Another theme is history. Machiavelli identifies other leaders throughout history, from contemporaries in the Italian city-states, to Roman leaders from antiquity. By using concrete examples, Machiavelli is not writing an abstract treatise; rather, the book is more like a practical "how-to" for the ideal prince to govern.