What would have happened if the Lords Declarant had called their banners and marched for Robb?

[Aenarion]

Obviously they weren't the Lords Declarant at that point. That being said, what would have happened if those lords called their banners and marched for Robb Stark and Riverrun when the war started? 

The Royces, Templetons, Waynwoods, Belmores, Redforts, and Hunters call their levies and knights and march. Maybe the Corbrays come into it somehow. What happens when the Young Wolf has two and a half large armies? (23k from the North + Freys, 11k from the Riverlands, and another 15 to 20k from the Vale sounds about right?) 

Does he send his foot over to the Vale army, and order them to march against Tywin Lannister (now to a much fairer fight), and take his 6k cavalry against Riverrun to start with? 

[Scorpion92]

I think Robb would have asked experienced commander like Lord Yohn Royce to sail from Gulltown to White Harbor with significant force to help with ironborn attack. Rest of Valemen would have bolstered Robb's army in Riverlands.

[Aenarion]

I meant if they declared, and marched at the start of the war (before the ironbon attacked).

At that point it's pretty obvious that sending a good commander like Bronze Yohn with a medium sized force to put the ironborn in their place would be a good idea. 

[Curled Finger]

Would the LD go against Little Finger?  What damage could he do in their absence?  I'm thinking 15 to 20,000 fighters is right in the neighborhood, but what happens to the families those Lords leave behind?    Would Anya Wainwood, an old woman, go on a march?  Supposing she does, who remains to protect the people of the Vale from Little Finger?   As evidenced in the Corbray marriage, Little Finger has friends everywhere including wealthy merchants who would be willing to pay to take those lands and castles.   Without Lysa or the Blackfish, what reason would these people have to join in Robb's war on the throne?   

As enticing as it is to imagine a solid defense in the North, why not just take the Vale fighters in tow and send the Northerners home to defend their own land?    The LD are a prickly proud bunch, a bit holier than thou, they would not consent to support a party they had no interest in when the crown's war has not infringed on their lands.   They most definitely wouldn't join a war to be a back up act.   Their resources are far too precious and their potential losses would be nearly incalculable if they sent a real force off and left Little Finger unsupervised.   Robb's rebellion was the wrong time for the Vale to show force.   The right time for them to send a smaller force would have been after the Red Wedding to wipe out the Freys.   I was surprised they didn't demand it in negotiations with Little Finger.   We shouldn't forget that Robb and Cat and Edmure are the Vale's Lord's kin.   It says a lot to me about the Vale's sense of righteousness that they didn't march on the Twins to avenge Sweet Robert.   Perhaps they may yet, but they don't strike me as people who genuinely have a global conscience.