RandV
It's a wolf v2.0
Tywin's war council at the end of season 1 is suggesting they approach Robb and cut a deal since they are surrounded by enemies and need to save their army to hold onto what they have, and Tyrion correctly points out that Robb won't come to the table because he's winning and he's angry about Ned being executed. The possibility was definitely there to go try and cut a deal prior to the Tyrells joining with the Lannisters. Being named, and accepting, King in the North really limited Robb's options for alliances with the Baratheons as well.
Ah right that's what you were talking about. Although at that point the conflict was a spat between the Lannister's/Tully's/Stark's, while everyone in the South was distracted with the death of King Robert leaving several contenders vying for the throne down south.
What I was more getting at is that once his bannermen declared him "King in the North" (can he even back down after they do that?) that changed everything. Trying to rule Westeros from the Iron Throne without the Targaryan's dynasty is a very precarious position, because you have a continent that used to be divided into separate Kingdoms being ruled by 8 great families and now 1 of these 8 has to hold the other 7 underneath them. This was something Robert said in season 1, 'there are 7 kingdoms to rule*, 1 king'.
The way to accomplish this is by having a centralized alliance that will step up and smack down with force anyone who tries to break away, like the Greyjoys did. If you have 2-3 houses united behind the throne then you can keep the rest of the houses in check because they are naturally divided. But the key to this is you can't just let one house break away or you risk a snowball effect.
*Riverlands/Tully's are one of the 8 great house but don't get counted in the kingdom count because they had been conquered by the Iron Islands when the Targaryan's invaded.