About the War:

[Insomniac]

So, i'm very new in The Witcher saga, never read any books and just have finished the second game. so, i have a question: What's happening between the Nilfgaardians and the Northlings?
what is this war that everyone talks about?

Also, sorry for my English, not my home language.

[Hashbrown]

nilfgaardians are responsible for the events in the north, also hired letho to weaken the north. Now they are invading.

[BadgerMilk]

Nilfgaardians are like the romans and want to rule over everything.

[PuppyFiddler]

Watch game of thrones, lol. Basically the empire is using the in-fighting between the northern kings as a chance to invade a weakened territory and used the elves and witches and that letho witcher fella to make it happen by killing the kings. The elves are pissed off because everyone has abused them at some point. Should be interesting to see what the sorcereses are up to in TW3 seeing as they've probably gone underground.

[Phex]

@Hash, that's a huge spoiler. You should have used the spoiler option there to warn those who still haven't completed the plot.
As per the Nilfgaardians, well there are several aspects to this.
First of all you should know what Nilfgaard actually is;
They are a huge united empire in the south. They are very symbolized and in a lot of ways represent the future, counter to the north kingdoms representing the south.
But of course there are some problems therse as well, Nilfgaard has some very strict social rules, essencially everyone is united by being under the empire's control
example - Nilfgaard has such institutions as citizens spying on one another and a secret police
Nilfgaardians don;t have the same personal rights as the northeners do. In the south you have to behave properly - think the victorians - everyone has to dress, speak and act respactably.
On another flipside - Nilfgaard has no persecution of non-humans. In fact the emperor and therefore the empire itself have a high opinion of the elder races, there thet are not only accepted but also valued.

[Phex]

This might take some more bulk text so i'll split it so as not to spam.
Nilfgaard hasn't started to try and rule the north just now, when they are weakend.
In fact they tried once before - at the battle of brenna and were beaten back.
Their aim is to rule, whether they do so by exploiting a weakened north or not - that matters litte to them , althought hey will certainly take advantage of the situation.
There is also another thing. The prophecy of Itlina - which says that the end of the world is coming - some believe that the emperor wants to unite all of the kindgoms under his rule because he thinks that only together will they survive this end of the world.

[Phex]

So there you are. Some facts to think over as you decide what you, and by extension your geralt thinks of the empire. Are they good evil, neutral, the enemy, a necessary evil, the way foward?
Who knows? No one, but in the new game you will probably be called upon to make up your mind on the matter.

[Phex]

Let me just respond so some previous arguments so that i can finish up my contribution to the topic.

@Hash " (they) are responsible for the events in the north" yes and no, they provoked them, that's for certain, and they supported certain parties, but you could easily make the argument that they only provoked the conflicts, the north did the rest. All they needed was an excuse.
Important plot detail Seila and other actually wanted Demavend dead and would have killed him even without letho's involvement

@Irish "Nilfgaardians are like the romans and want to rule over everything." Well again, this is a yes and no situation. Keep in mind that like with most factions in fantasy books, Sapkowski (the author) put the nilfgaard empire together from parts of differenc civilizations as well as his own imaginations. Therefore it's hard to make a direct link to just one civilizations.
Still, you can see some elements of the romans here, the empire is, well an empire in name, it's militaristic, advanced and very much united.
However social norms would point more to the victorian english empire
The spying on citizens element would suggest links to more recent political fronts.
In the end the empire is most likely and amalgamation of all of the things which the author and indeed us,the educated reader/player connects to the idea of an empire.

@Puppy I'm going to have to be a right, two handed bastard (sword) here. I'm afraid that while it;s hard to say what historical periods, factions nations were melded into the idea of the nilfgaard empire, the war of the roses is one of the ones which are definitely wrong.
You see the game of thrones was based on the english civil war known as the war of the roses.
If you are a fan of the series you might want to read up of that war, you'll be suprised how much martin ripped out of history, often without making any significant changes.
But in any case, the war of the roses was a persiod where houses battled with one another for political power. This was a period where it was said that chivalry died - essenciall where the fantasy world of knights and heroes turned into the grim dark fantasy world not unlike withcer.
It was a time of horrible brutality or unyielding opportunism, for the first time no mercy was given and any advantage was taken no matter the morality of such an action.
We can extend this to the stage of the northern kingdoms in the world of witcher, and it works quite well, the kingdoms seem to be constantly in conflict, attacking one another and using any means to win, be it war, politics or treachery.
HOWEVER - and as the caps notes, this is the northern kingdoms.
Nilgaard is united and very different, the metaphor of the game of thrones is certainly very wrong here.

[PuppyFiddler]

@Phex Christ it wasn't to be taken completely seriously, hence the "lol". HOWEVER, regardless of being united or not, Nilfgaard is like the empire in GoT wanting the northern kingdoms fighting amongst themselves to weaken them in order to extend control.