As soon as Ned Stark was captured by Joffrey, Robb Stark gathered all the leaders of the most powerful houses of the North and started marching towards King's Landing, apparently motivated by the captivity and then death of his father. What were his true motivations anyway?
Is this rebellion meant to turn the North into an independent realm which can be referred by Robb been called "King in the North" by his allies, or simply to take the Iron Throne?
We know that he sent his mother, Catelyn Stark to propose an alliance with Stannis and Renly who were also involved in the race to the throne. So maybe at that time, he had no reason to have any claim regarding the Iron Throne, but it seems that things get more serious as the story goes on and that he eventually, before his death, wanted to become the "one true king" like Stannis did. So in this case, what changed his mind?