Given the complete change of the war from the books and the TV show. Here I shall be putting up brief descriptions of the battles from the Game of Vengeance and Justice, mostly for my own benefit as it allows me to keep track of numbers remaining in the various armies of the war for story purposes.
I shall be starting with the first battle of the war.
And the ... in this first section represents the division between the two sides.
The Battle of Harrenhal.
Conflict: The War of the Four Kings
Date: 298 AL
Place: Harrenhal
Result: Stark Victory
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-Combatants-
House Lannister... House Stark, House Tully
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-Commanders-
Ser Jaime Lannister ...Lord Robb Stark, Ser Brynden Tully
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-Strength-
15,000 ...25,000
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-Casualties-
Almost total, fifty high-borns taken hostage... Minimal, less than 1000
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Prelude
Following the capture of Ned Stark, Robb called his banners and rushed south with 18,000 men to free his father. He met no opposition as he rushed down the Green Fork, however there was troubling news from the west.
Ser Jaime Lannister, sent by his brother Tyrion to Casterly Rock, so that rumours of his incest with Cersei did not spread, informed his father, who mobilised two hosts of men, fifteen thousand under Jaime and another twenty five thousand under his own banner. They rushed across the border with the Riverlands and, whilst Tywin moved at a slower pace, so as to prevent the Riverlords from mobilising their men in support of their Stark allies, Jaime rushed ahead to block the route for the Stark host and defend King's Landing.
However, whilst the Riverlords in the west were unable to mobilise due to Tywin's presence, those in the east did, under the command of Ser Brynden Tully, who had resigned his position as Knight of the Gate to lead the Rivermen in defence of their lands. He was able to marshal a small host to defend them, but it was not enough to face Jaime, the main opponent of the Lannisters were the Starks, currently north of the Ruby Ford, the main route from their current position to the capital.
Jaime, hoping to seize a strong base from which to halt the Stark's, knowing that, should he try to guard the ford, Ser Brynden would attack his rear, lay siege to Harrenhal, with Lady Whent only just managing to gather enough men and supplies to her to hold out. This gives the Stark and Tully hosts time to link up and march on Harrenhal together.
The Battle
Playing of Jaime's inexperience as a battle commander, Robb organises an attack on every portion of Ser Jaime's host, which had to split into five separate camps in order to effectively siege the great castle. He orders a Tully attack to strike the camp next to the one where Jaime was. This provoked Jaime into retaliating, hoping to destroy the weak Tully force before he had to deal with the Starks. However, Robb launched his assault and with a strong horsed contingent, was able to capture Ser Jaime, leaving his forces leaderless as Lord Umber and Bolton swiftly overwhelmed the Lannister camps that they attacked, scattering the few survivors to the winds. Only the camp that opposed Lord Karstark made any form of resistance, able to rapidly form a shield wall. However, the garrison of Harrenhal sallied out and took the wall in the rear, breaking it and bringing a total victory to the Starks.
Aftermath
Robb, previously underestimated as a battle commander due to his youth and inexperience, sends shock waves amongst the Lannisters from King's Landing to Casterly Rock. Unfortunately, news of the capture of Jaime and the defeat of his host arrived at the capital too late to prevent Eddard Stark's rash execution, and the road was almost completely open for Robb to march on the capital if he wanted.
However, Tywin Lannister was still in the field with better soldiers and he himself was a far better commander. Although he ceased his advance on the Starks and began to retreat, he savaged the countryside, hoping to lure Robb to him rather than have him march on the capital. But his position was untenable. Robb had inspired the Riverlords to gather and, at Riverrun and at Raventree Hall, two hosts were emerging, forcing Tywin to retreat or be surrounded on three sides by hosts beset on vengeance. He began his retreat to the Golden Tooth.
Robb was declared King in the North by his bannermen in the ruins of Harrenhal. Days later, the Riverlords removed themselves from the Iron Throne as well, when it became clear that the Iron Throne would not punish Tywin for his illegal incursion into their territory. Ser Edmure Tully, acting in place of his ailing father, placed the Riverlands under the suzerainty of the Kingdom of the North.
