1. Executing Rickard Karstark
After Rickard Karstark murders a couple of Lannister boys in revenge for his own sons death at the hands of Jaime Lannister, Robb executes him, believing it to be the honorable thing to do. While one can understand why Robb did it, he needs to stick his honor to a degree and handle things according to the law, hes also in a war against the Lannisters. Theyre not the most honorable bunch, and perhaps Robb needed to get his hands dirty as well. It may have been smarter to let Rickard live and keep the additional manpower. This loss of troops is exactly what motivates Robb to go back to Walder Frey for support, eventually leading to the Red Wedding. Not only that, but it is this exact loss of troops that encouraged Walder and Roose Bolton to betray him anyway. They want to play for the winning side, and seeing as how Robb was losing support, they decided to jump ship. A jerk move, no doubt, but you can see how, in the interest of self preservation, Walder and Bolton figured it was the most logical move. Do you agree or disagree? What, in your opinion, are the biggest mistakes? Feel free to comment!