Yes it's very subjective , but for me Nilfgaardians are like a mix of the worst aspects of the Teutonic armies who slaughtered so many innocent people in the Middle Age in their drang nach osten (despite being defeated by A. Nevsky and the people of Lithuania ) , killing civilians for free or just because they were pagans , and the nazis in WWII with their intolerance , racism and slaughters of million of innocents
You haven't read the books have you? Sapkowski's world is not so black and white as you make it look like. Hell, half of the saga takes place in Nilfgaard and Geralt and Ciri are not there to kill Nilfgaardians.
Niiflgaard persecuted mages (ok for some it's acceptable , but they persecute them by principle , out of idelogical belief , not because mages are deemed evil or did something wrong or something , they re simply anti-magic , anti elves , anti everything that is not Nilfgaardian or sanctionned by the Emperor and useful to him , similar to a fuhrer basically because he has no counter-power like Temerian king needs to negociate with its council and nobles , the Emperor of nilfgaard seems like an absolute ruler )
Sigh... I'm gonna have to spoiler the books to prove you wrong.
Anyways, the hatred of mages is not ideological, it is a personal vendetta of the emperor. A mage turned him into wereboar when he was little. It was decades later that Geralt lifted the curse.
The emperor believes in Ithlinne's prophecy of White Frost that's coming to consume the world, so he is pursuing the Elder Blood for the power of traveling the worlds. He intends to save the human race from what was depicted in the end of Witcher 1. How altruistic that really is... well your guess is as good as mine.
And during the peace treaty of Cintra he agreed to give up a lot of conquered land on the advice of Merchants Guild who suggested that the best course of action would be to overtake the Northern Kingdoms economically. It could be that this is out of the window now with troops crossing Yaruga again.
Also they persecuted and betrayed Elves (Iorveth tells us ) , gave them a small place to live but where they aren' free and are excluded elsewhere ( abit like WWII jews ) and treated even worse than in the northern kingdom where they can at least live alongside humans even if there are stil racists in Temeria , Redania etc ... well just my understanding
This is completely wrong. Nilfgaard is the only country in the world that is even willing to make any kind of treaty with the elves. Or to treat them as equals. The fact that they gave Dol Blathanna to the elves is utterly unprecedented. And it was completely free until the peace treaty of Cintra where a lot of compromises were made. Elves got fucked over there, yes. The territory was turned back to Demawend as a vassal state. And one of the conditions was that the Scoiatel units were declared as outlaws. So yes, Iorveth can't go there.
There are still many elves in Nilfgaard. A part of their army consists of elves. I don't think there are any nonhumans in the armies of Northern Kingdoms.
Also in game at some point , we are told " if that happened in Nillfgaard
, you would be hanged already " , so it is suggested Nilfgaard is a very intolerant country with very harsh laws and rules , with a ruthless ruler obcessed about expansion (like Henselt , but Henselt use Fair means and really seems like a frank and direct person , real archetype of the Celtic warrior who wants a worthy adversary and would never backstab dishonourably , for instance he burned Sabrina when she acted unfairly (she basically used the "nuclear " option if we make an analogy with our times ) , whereas Nilfgaardian (just like the Lodge ) seem to stop at nothing machiavellious or simply treacherous to achieve their goals as we see in the plot with Shilard and Letho , a bit like Hitler revoking treaties and making up excuses to invade Poland and arguing being the victim when he was the aggressor (Letho makes me think of Otto Skorzeny , who tried some interesting things in WWII behind enemy lines )
Henselt is rather different in the books. He conquered Aedirn from the north while Aedirn army was battling Nilfgaard in the south so honor is not that important for the dude.
Though later when Nilfgaard turned on everybody in the North then he did send his troops to battle Nilfgaard. Zyvik was at the battle of Brenna for example. ;)