The next thing we learn is that thugs will always try to cloak their atrocities under the veil of "it was required for the benefit of humanity" as Caesar likes to say. Also we learn that you simply cannot trust folks like Caesar like the 86 tribes he conquored did and ended up as slaves with their histories cultures completely obliterated by the Legion.
We learned that the NCR and many nations like them will take whatever they want simply because they can and will try to cloak it in the guise of nationalism. Hence they wanted to take Hoover Dam and use it to control everyone in the Mojave including those on the strip and the surrounding communities.
We learned that people who say thay are the beneficiaries of mankind are only tyrants of a different stripe. Mr. House is a good example of this.
The final thing we learned from FNV is that if you want to be truly free you will have to fight for it and it is never free. The price of freedom is tremendously high and the fee is always paid for in blood both innocent and guilty. Thus if you are not prepared to pay the price for your freedom then you are doomed to remain a slave.
Honest Hearts taught us 2 things.
The first is that even the worst of us can be brought back from their acts of savagery ... dare I mention the Burned Man.
The other thing we learned is that you cannot negotiate or run from those that are driven by hatred and only seek your destruction. The White Legs fit this description nicely. The only solution available is their complete destruction otherwise they will simply bide their time and rebuild their strength and follow you whereaver you go and try to destroy you at a later date. This fact has been nicely illustrated by the failure of the NCR to obliterate Caesar's Legion after the first battle of Hoover Dam so now they face an even stroger Legion today. The only way to be truly free of Caesar is to eliminate him and his generals and then annihilate the remainder of his Legion and free his slaves.
