[cape_royds]

I vote for the Astapori slavers, who made the single biggest blunder of any of those listed.

But Robb Stark is a case study in political folly, which is worth examining in some detail. The breaking of the Frey alliance, and sending Theon as an envoy to Pyke, are well understood errors.

But perhaps Robb's worst mistake was in letting the Greatjon bellow, "King in the North!"

There is more than one way to lose control of your bannermen. The most obvious way is through their insubordination, but Robb's crowning showed us another way of bannermen usurping authority from their liege.

By letting his lords crown him while in their cups, Robb lost any control over his war aims, and thus enormously complicated his own strategic predicament.

How could he ally with any of the Baratheon claimants, or with the Tyrells, after repudiating the Iron Throne?

This momentous decision--a transition from limited to total war, meanwhile forsaking any allies--was made without a minute's reflection on Robb's part.