This
I
the only name I could recognize in there was Nilfgaard :/
Simplifying Witcher 2: divide the northern realms into quarters and it looks like this.
Redania: King Radovid | Kaedwin: King Henselt
---------------------------------------------
Temeria: King Foltest | Aedern: King Demevend
Demevend is the first to die, in the intro movie before the game starts. Foltest dies next in the prologue.
Radovid wants to secure as much of Termeria as he can after Foltest death, same for Henselt and Aedern. Upper Aedern is the area that sits on the border of Kaedwin, and Henselt is trying to claim it. Saskia is a freedom fighter, also a shapeshifting dragon, trying to secure Upper Aedern as a "Free State" for outcasts and persecuted.
Flotsam is a river town more or less in the middle bordering all four kingdoms, so everyone wants it.
Depending on paths and choices Radovid could be the only king left alive. Termeria could be halved between Radovid and Henselt. Henselt could take Upper Aedern, or lose.
Either way Termeria and Aedern, being the south most kingdoms before you hit Nilfgaard, are the first to fall in the invasion.