"The thing is I don't think Robb deciding to go along with his bannermen and be crowned the King in the North."
This was a mistake, because it meant it was impossible to become an ally of Stannis or Renly.
"I think the strategic error lay in accepting the riverlords as vassals, however."
Sure doubling the size of your army is a bad idea *sarcasm*
"If he could withdraw beyond Moat Cailin, I'm sure the North could have remained independent."
You forget his reason for going to war, his father and sisters were taken hostage in Kings Landing and we was told to come south and swear fealty to the crown. He called his banners with the sole purpose of getting the crown to release his father. Once his father was killed, his people recommended he be king in the north.
Calling your banners and staying at Moat Cailin doesn't bring his father back, marching south does.
"But as soon as he committed to holding the riverlands, the game was practically up."
No, he was winning until the Reach declared for Joffery.
"While I say Robb beelining to KL and blocking Tywin at Blackrush River on the Goldroad as the best chance, I don't say it's a good one. "
Again, look at where harrenhall is, look at were riverrun is. If he tries to march on Kings Landing, Tywin will get there a good month before he does. Tywin on the walls can defeat any army 10 times his size, the book says as much.
"Either choice Westerlands or Crownlands have daunting strategic problems for Robb. And since the book goes with the attack the Westerlands..."
No, the westerlands was a good choice. I stand by that.
"Joffery, the whole reason that this war is being fought would force Tywin at Blackwater Rush River anyways"
You've played the ck2 mod, and seen the show, but have you read the books? I doubt it based on what your saying. Even so, lets play multiplayer CK2, I play as the lannisters, you play as the the north, and you try your beeline strategy.
It will only work because:
1. Tywin can't hide behind the walls of Kings Landing
2. Stannis/Renly will ally with Robb in the siege.
"SPOILERS!!!!
Ends horribly for Robb
END of SPOILERS"
MASSIVE SPOILER FOR EPISODE 9 OF SEASON 3. I REPEAT I AM GOING TO TALK ABOUT EVENTS THAT HAPPEN IN SEASON 3 EPISODE 9. IF YOU DON'T WANT TO KNOW WHAT HAPPENS IN THAT EPISODE UNTIL IN PREMIERS IN A ON MAY 26TH THEN DON'T READ BELOW!
It ends horrible for Robb because the Freys rebel against him after he marries Jeyne Westerling (he was bethrothed to Roslin Frey in book 1), and he is killed by the Freys, not by the Lannisters. Also Roose Bolton intentionally had intentionally had 8000 men killed in 2 losses to Tarly forces, first at Duskendale and second at Ruby Ford. He did this intentionally because he wanted the north to have as few soldiers as possible for when he and the Freys rebelled.
He was winning the war until:
a) Edmure Tully ruins his plans by focing Tywin out of Harrenhall to retreat south.
b) He married Jeyne Westerling which caused the Freys and Boltons to betray him.