Start of War
Following the first two wars, the Northern Kingdoms were left devastated economically. This led to increased civil strife and religious fanaticism, in particular for the Cult of the Eternal Fire. Simultaneously, the rulers of the North used the non-humans as scapegoats for the worsening state of their kingdoms. This contributed to the continued guerrilla activity of the Scoia'tael, further weakening the north.
In 1271, after the assassinations of Demavend and Foltest by the Kingslayers, the remaining Northern kings, sorcerers, sorceresses and Nilfgaardian ambassador, Shilard Fitz-Oesterlen, assembled in Loc Muinne. The assembly was to decide the future borders and powers in the Northern Kingdoms following the recent regicides, as well as restoring the Council and the Conclave of Sorcerers. However Letho of Gulet, working for Emhyr var Emreis, was able to pin the blame for the deaths of Foltest and Demavend on the Lodge of Sorceresses, which led to a witch hunt in the North.
Break of warfare
At first, Nilfgaard's offense carried on without much resistance from the Northern Realms. Due to Demavend's assassination by Letho of Gulet and Prince Stennis either dying or fleeing, Aedirn was left in an unstable position. Lyria and Rivia, being almost entirely dependedent on Aedirnian commerce, fell almost immediately after the invasion started, with Queen Meve going into hiding. The leaderless Aedirn would fall shortly after.
Regardless of Temeria's fate from The Witcher 2: Assassins of Kings, John Natalis, the Hero of Brenna and a veteran of both Northern Wars, rallied what was left of the Temerian Army to fight against Nilfgaard. They managed to halt the Nilfgaardian advance northward for 3 days before being overwhelmed, resulting in Nilfgaard breaking through and the Temerians adopting a guerrilla campaign against Nilfgaard instead. John Natalis subsequently disappeared and was not seen nor heard from since, though survivors claim he did not fall in battle and simply vanished without trace.
In Spring of 1272, Nilfgaardian troops commanded by Peter Saar Gwynleve conquered White Orchard during a last battle and then headed to Velen. Phillip Strenger, nicknamed the Bloody Baron, used this anarchy to assert control of Temeria's leaderless territory in Velen. In return for his alignment to Nilfgaard, he was promised the title of ruler over Velen after the war ended by the new Field-Marshal Havart var Moehoen. Some Temerians, like those led by Roche, fled northward to the highlands on the Redania-Temeria border, where they harassed Nilfgaardian transports, patrols, and supported the Redanian military in the conflict.
Earning the ire of both sides of the conflict, King Tancred Thyssen of Kovir has pledged neutrality, unlike his father who supported the Northern Realms at least indirectly through financial loans and mercenary companies. He has also opened his realm to all mages, including those belonging to the ostracized Lodge of Sorceresses, who were implicated by Nilfgaard in a plot to destabilize the North, leaving it weak to its blows. Tancred did, however, divide the quarreling Hengefors League with Redania, with Kovir taking the majority of the dissonant realms.
After easily conquering half the North within merely two to three weeks, the Nilfgaardians invaded Kaedwen and believed that Radovid would be intimidated enough to sue for peace, so they waited for the first snows. Instead of acting as expected, Radovid used the winters as time to invade Kaedwen and either killed Henselt on the battlefield and assumed control of Kaedwen's army and defense, or attacked a kingless Kaedwen, (whose defense was going poorly thanks to their lack of a clear ruler), and merged the reinvigorated Kaedweni army with his to drive Nilfgaard from Ard Carriagh. As a consequence, instead of having two weak adversaries, the Nilfgaardians had to contend with one strong enemy.
In Velen, a massive but indecisive battle took place, during which The Order of the Flaming Rose was sacrificed and their remnants mockingly given a series of foothills and swampland north of Oxenfurt for their "important sacrifices on the battlefield". Meanwhile, their armories, treasuries, and estates were seized by the now-militant Church of the Eternal Fire, leaving them with practically nothing. The Redanian Army took control of the offensive, which pitted them against Nilfgaard's armies in the mires of Velen. At the end of the battle, both sides retreated; Redania remained on the north side of the Pontar, ready for another Nilfgaardian offensive, while Nilfgaard stayed on the south side of the river, awaiting reinforcements from the heart of Nilfgaard (which the Merchant's Guild and noble houses were constantly blockaded from going to the frontline, due to frustration Emhyr's conquests northward which had always ended in failure).
Status quo on Pontar
While Emhyr was waiting for forces from the south to defeat Radovid, and Radovid tried to press the Nilfgaardians by funding and arming Vernon Roche's Temerian resistance group, both rulers turn their eyes to Novigrad: a rich, Free City on the Pontar River which could provide men, ships and most importantly, gold, to whichever side possessed it.
In the meantime, Novigrad had fallen under the influence of the Church of the Eternal Fire; this was partly thanks to Radovid's influence, who, in collaboration with Caleb Menge, sought to crush opposition in order to make it easier to seize the city. Novigrad's population of non-humans and magic users were being held responsible for causing the war, envoking a major purge with Radovid's approval, carried out by the witch hunters, who acted as the enforcers of the Church.
In Kaedwen, Nilfgaard's armies besieged Ard Carraigh and engaged Radovid's forces in a series of battles. The fighting was implied to be particularly brutal here, as it is mentioned by several Redanian soldiers. Additionally, Ban Gleán was said to be attacked frequently by the troops of General Voorhis, but without much success due to it being a fortress that stations a huge number of mercenaries. There was also a guerrilla campaign in Kaedweni wilderness, making the fighting even more difficult for the Nilfgaardians.
The War's End
If Geralt doesn't take part in Radovid's assassination (default): Owing to his superior tactics and leadership, Radovid defeated the invading Nilfaardians, absorbing all of the North under him and turning it into a Northern Empire. In his new empire, Radovid spread his witch hunts all across the North, burning all non-humans, mages, herbalists, soothsayers and anything alien to humans. In Nilfgaard, due to dissatisfaction with the Empire's failed wars in the North, Emhyr var Emreis was killed by internal conspirators and succeeded by Morvran Voorhis.
If Geralt helps to assassinate Radovid but lets Dijkstra kill the Temerian patriots: After Radovid's death, Dijkstra took control of the North and managed to defeat the Nilfgaardians. He subsequently unified the Northern Realms, transforming them into a powerful empire rivaling Nilfgaard. Dijkstra believed that, for long-term survival, modernisation would be necessary; he began a campaign for industrialisation, technological advancement and strengthened the military, but also allowed magic in the north. Many of his liberal and progressive policies often contravened the will of the general populace, but they went ahead regardless. With Nilfgaard having lost the war, Emhyr var Emreis was killed by internal conspirators and succeeded by Morvran Voorhis.
If Geralt helps assassinate Radovid and saves the Temerian patriots: Left practically leaderless, the Northern Realms were ultimately conquered by Nilfgaard. However, Temeria became a vassal but sovereign state after negotiations with Nilfgaard during the war, while Kovir was left untouched after signing a peace treaty with the Nilfgaardian Empire during the days of the first war. After achieving victory, Emperor Emhyr initiated a sweeping purge to all those who opposed him, consolidating his rule over the empire.
- If Ciri becomes empress: Afterwards, Emhyr ceded the throne to his daughter, Ciri.
- The Northern Realms
- Redanian Armed Forces
- Temerian Armed Forces (officially destroyed early in the war, assists Redania via guerrilla warfare; halts operations against Nilfgaard after negotiations)
- Kaedweni Armed Forces (via Redania)
- Witch hunters
- Council and Conclave (optionally)
- Order of the Flaming Rose (disestablished after the Battle of the Pontar)
- Aedirnian Guerillas (allegedly)
- Nilfgaardian Empire
- Nilfgaardian Army Group Center
- Impera Brigade
- Nausicaa Cavalry
- Northern Volunteers
- Northern War III occured only in the game continuity. In the novels, the last Northern War was the second, which ended in 1268.