The Red Wedding was Provoked by the Secession

Orginally posted on Quora to answer Why Did Walder Frey betray Robb Stark?

Frey lands form, ironically, a kind of bridge between the riverlands and the north. There was no way a north-riverlands secession the map could be drawn without Frey. The secession also constituted a new arrangement and also a new level of rebellion against the crown. It was a major insult that Frey lands were assumed included without his being courted and a new toll being paid. At least that is how Lord Walder saw it. Since Edmure was Lord Walders' liege, Robb did not see a need to deal with Lord Walder separately, especially since many Freys laid down their swords and swore him fealty when he was crowned. So many river lords and northern lords were present and voted by laying their swords at Robb's feet that Lord Walder was outvoted by his region.

The thing to understand is how fundamentally in the wrong Lord Walder Frey is and how opportunistic his view of his position is. One of the reasons the Freys are looked down on by older houses is that their house philosophy is inherently mercantile. Lord Walder sits on his bridge, as if beside his wares, waiting for a customer to make him an offer. Then, he haggles. That's not allowed. Regional powers own the loyalties of lesser houses and may assume fealty based on nobility and tradition. It's as if your neighbor in an apartment complex thought he got to require a toll for you to pass through the hallway in front of his door, despite your paying rent and those being common hallways. Except that the Freys may argue that they built and maintain their bridge and own the land it's on. It's the kingsroad that's the common hallway. But the king owns all the lands, including all the bridges. So, you can see how there would be a basic and problematic disagreement about how things should be done between everybody and House Frey. There's a real sense in which Frey is in the wrong, but in another real sense, the bridge's location ensures no king is ever going to show up insist a particular individual be allowed to cross. So, Frey gets to keep requiring a toll.

Lord Walder, characteristically and wrong-headedly, lashes out at those he feels to be getting too big for their britches, especially if he feels them to be taking him for granted. He expects to be approached with offers and resents it when someone he thought would make him an offer doesn't. Wrankling at the Tullys for snubbed wedding proposals and invitations, Walder refused to send aid to Riverrun against the Lannisters. But he switched sides in a snap when he felt Tywin to be taking his support for granted. Lord Walder tells Catelyn his reason for meeting with her at all to even consider offending the crown by allowing Robb's army to cross is that he'd been waiting for Tywin to ask him to betray his allegiance to Tully, and he hadn’t. Lord Walder seethes:

“Lord Twyin the proud and splendid, Warden of the West, Hand of the King, oh what a great man that one is, him and his gold this and gold that and lions here and lions there. I'll wager you he eats too many beans and breaks wind just like me, but you'll never hear him admit it, no. What's he got to be so puffed up about anyway? Only two sons, and one of them's a twisted little monster. I'll match him son for son, and I'll still have nineteen and a half left when all of his are dead!” He cackled. “If Lord Twyin wants my help, he can bloody well ask for it.”

Lord Tywin should have asked for what help exactly? Oh yes, against the Tullys. Help that would have been most useful in the form of treachery against his liege lord. This is what I mean when I say Lord Walder always meant to betray Robb. He always meant to betray Tully and Robb came with the Blackfish and Catelyn to aid Riverrun.

Yet, Lord Walder aids Robb to lash out at Tywin the same way he, moments before, aided Tywin to lash out at Hoster. Being irascible is part of Lord Walder's haggling style. He crosses his arms and plays prickly so as to get a better deal. But he really feels it. And treachery is an assumed part of the Frey children's game Lord of the Crossing, where players try to sneak in the idea of “mayhaps” and the lord gets to knock anyone into the water he can reach with his stick.

So, when Robb made himself king of a map that included Frey without even bothering to ask if he'd like to be a part of such a kingdom, if he'd be willing to defy the crown to such a purpose, and what he'd require as payment, it woke Lord Walder's ire. That opened the way for Bolton to propose the Red Wedding.

Lord Walder's original plan to betray Robb and the Tullys, one he actually did carry out, only involved secretly returning to the king's peace as soon as negotiable. When, in an Arya chapter of A Clash of Kings, we see two Freys arrive at Harrenhal with a chest of gold and leave with the four Freys captured at the Green Fork it means Lord Walder betrayed Robb. Tywin doesn't release captives for gold alone. And, as we hear from Wyman Manderly, Tywin undermines his enemies by writing to their bannermen with carrot/stick proposals. So, when Tywin took four Freys captive on the Green Fork, it provided pretext for Walder to make contact and a new arrangement.

Frey was always going to go back to Tywin, but he wasn't always going to host a massacre of northmen. Based on when things happen, it's obvious the Red Wedding's broader strokes were planned and in motion long before Robb marched on the Cragg. It could not have been Robb's breach of contract with Frey by marrying Jeyne Westerling that prompted Lord Walder to decide to kill him. That was an after-the-fact pretext.

The Red Wedding was Bolton's idea to forward his ambitions in the north. Its primary purpose was to kill off the northern armies so they couldn't return home. Robb had to die but so did the thousands who would have accompanied. When Bolton wed Fat Walda, it was as part of a deal with Lord Walder that included the Red Wedding in some form. Bolton then sent Tallhart and Glover to Duskendale on orders he pretended came from Robb, to feed them to Tywin. All this happened after Frey had ransomed the captives back. Lord Walder presumably wrote to Tywin, requiring Riverrun for Emmon among other things, in exchange for ending the northern rebellion at a dinner. Tywin also got a letter from Sybelle Spicer, saying she had Robb drugged in her daughter's bed. So, the Red Wedding betrayal was several loose conspiracies and a few tight ones. Still, Lord Walder wasn't so much angry that Robb had broken the engagement as looking for a way to vent his long held resentment toward the Tullys and his specific ire at Robb's having taken his allegiance for granted when the north-riverlands secession was voted on.

The scene where Robb is crowned happens at the end of A Game of Thrones. It was toward the depressing end of a long night of drinking. Nobody knew how to make it okay that the riverlands had been burned or that so many, including Ned, had been killed. They had to ride hard at Lannister or feel they'd failed, even though they were on a winning streak, had retaken Riverrun and continued to stand in proud defiance. Despite Catelyn's arguments that more death and destruction wouldn't bring back the dead or replant the fields, the anger of those assembled ached for something to attack. The Greatjon's solution to declare independence struck an emotional chord that appealed to those assembled. They got to elevate Robb, who had earned their esteem, shake a fist at the crown, and swear to never bow to Lannister. But the idea that the riverlands and north could combine into a region is untenable. The north may stand in defiance, because of the Neck, but the riverlands will always be subject to the power of the crownlands because rivers are weak natural defenses and the crown can command numbers. The map and how it would really work wasn't at all considered. Neither was the ridiculous idea that it would give deadly offense if they didn't, as representatives of their respective regions, ask Lord Walder Frey for permission to secede.