Regarding Machiavelli (he's kind of my field of expertise)... if you're talking about "Il Principe" then you have to take into account, that it was written to a certain point in history for a certain person (or rather family) regarding by-then current events, problems and discussions. It was never meant to be a guide of everlasting value. That would go strictly against Machiavelli's concept of history and politics which he conceived to be dynamic and even organic. Apart from that he does state some things that are still true today, although the things about warfare may be outdated mostly.

What I learned from history? To quote a great spaghetti western: "One bandit is an outlaw, ten are a gang, ten thousand are an army! That is the goal! To overcome the limits of individual violence, which is crime, and get to the violence of the mass, which is history!"
In short: Just conquer enough land, butcher enough enemies and there will always be people defending, admiring and even praising you. (Machiavelli said something similar as he despised people (especially historians) praising tyrants)
Plus: There is no absolute truth in history, only certain numbers and facts which are being interpretated differently by different people (sadly very often along the lines of nationalistic nonsens).

Gosh, as I look upon my statement(s)... I seem to be quite bitter towards history.