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[GoT] Ser Jorah Mormont doesn’t develop feelings for Daenerys and allows her to be assassinated and returns home to Westeros. What happens next?
gpt
When Robb Stark calls his banners, Jorah Mormont responds. Robb is uncomfortable accepting the service of a man his father exiled, but a royal pardon is a royal pardon, and he can ill afford to refuse experienced men.

And Ser Jorah is at this point possibly the most experienced soldier in the Seven Kingdoms. While Westeros has enjoyed nine years of peace since the Greyjoy Rebellion, Jorah has been fighting his way across Essos as a sellsword in the Disputed Lands. He's been everywhere and fought everyone, and there's pretty much nothing he doesn't know about war. If Robb is smart, he'll listen to his advice and use him as a field commander.

Wild speculation, but Ser Jorah's presence could drastically alter the course of the War of the Five Kings.

If he had been in charge of Robb's forces in the Riverlands, instead of Edmure Tully, he would have had a better grasp on their strategy, and would have allowed Tywin to retreat west, preventing him from marching to King's Landing. Stannis would have taken the city and put Joffrey and Cersei to death, and the Lannister faction would be effectively defanged. The war could have been over within a few months, Tywin forced to sue for peace and Stannis reluctantly accepting a fragile detente with the King in the North.