Machiavelli comes up a lot: "Hitler was a Machiavellian ruler." We think of him in terms of "the end justifies the means," or "do whatever you have to do to rule effeectively."
He deserves the attention. Machiavelli almost single-handedly founded modern political thought as over-and-against classical politics. If you want to understand what happened in Western civilization in the move from Christendom to the modern state, you must understand Machiavelli.
Aristotle's politics was based on the notion that man is a political animal. There is a common good that brings human beings together in political communities, which are the only place that common good can be found.
Machiavelli starts from radically different premise. What human beings have in common is not a good, but only fears and self-interest. This suggests that, although he calls man a "political animal" as well, Machiavelli sees man rather as an apolitical thing. Humans have nothing in common but selfishness.
Politics, then, becomes something "effected by thought," not natural. The state is what the ruler creates in order to deal with the basic self-interest of his subjects. Thought is freedom and self-determination, not a way to discover what is good for all or what is the end for all human beings.
Machiavelli sees the idea of the common good as useless to solve the "problem" of politics--who has the right to rule? His solution is a kind of tyranny that actually gets rid of politics, understood as an observation of human community life, altogether. Force becomes the basis of society: "If we only had the power, we could fix everything!"
Remember that next time the power shifts in the House, Senate, or Executive office. Good old Machiavelli...