Which of Machiavelli's ideas did you find the most intriguing in The Prince?

Machiavelli's most prevalent and well-known idea is perhaps the most impactful, in large part due to its controversy. I will address this concept for those reasons and because I believe it is the most important.
First explored in The Prince, Machiavelli makes the controversial claim that the end justifies the means (though not is so many words), which can be stated as meaning that it does not matter the manner in which something was accomplished (especially from an ethical perspective) as long as the end result is positive and successful.
This concept has been used to justify many unspeakable acts and is one of the main arguments behind things like preemptive strike war policies, among many other terrible things. While these actions may seem to pave a road to accomplish beneficial things, they fly in the face of standard morality and contradict established codes of ethics.