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Given the following post, respond as if you're commenting on Reddit:
human
[GoT] King Robb of Winterfell sends Rickard Karstark to the Night’s Watch instead of execution. What happens next?
gpt
The Karstarks remain loyal to the King in the North, though Robb eventually comes to the realization that he still doesn't have enough forces to take Kings Landing.  They divert to Casterly Rock and take the Lannister homeland in a bloody battle.

Tywin is forced to make concessions and names Robb Warden of the North.  However, he's less than pleased after learning of the deaths of the Lannister boys who were Robb's prisoners.  He secretly makes deals with Walder Frey.

Robb brings his wife and army to the Freys for Edmure's wedding and victory celebration.  The Red Wedding occurs as before, the army of the North is scattered, and Tywin reclaims Casterly Rock.  Rickard is released and returns home where he holds a grudge against the Starks.