The book talks about politics and government. During his life, Machiavelli saw many changes in the government of Florence. He thought a lot about what a king or prince should do to make a strong government. In the book, he said the ruler had to get a lot of power.
One of the things he said that made people worried, was that ethics and politics are different. A person might have to do things that are wrong to get power, but with power he could then do good things. This thought made people upset.
Some people think that Machiavelli was being honest with his advice and saying what he really thought. Other people think that Machiavelli was playing a joke on princes who wanted too much power and did not care about what was right.