If Renly had lived, what would have stopped him?

[MichaelMjanovic]

Renly had the larger army and a seasoned commander like Randyll Tarly to lead his troops, if Renly so chooses. (Yes, I know he had Loras commanding) Stannis didn't seem to have a way to hold back his brother. Do you see any way that things don't end with Renly taking Kings Landing if he lived? Did GRRM just use him as filler?

Renly had the bigger army to be sure. Stannis had the rightful claim to the throne upon Robert's death. Renly would have had to battle Stannis in the first instance. Some alliance with Rob Stark would have had to made, most probably ceding the North. Woud Renly have paid that price? Maybe. The North together with Renly's host could well have vanquished the Lannisters. The end result? Renly: King of the 6 Kingdoms and Rob King in the North. In the longer term there would be further ramifications to be sure. Dorne, for one, would stir I think and agitate towards seccession.