Ned Stark is dead - executed in King's Landing after backing Stannis's claim on paper and opposing Joffrey.
Robb Stark is in the field as a Northern king-in-the-making after calling the banners.
Daenerys has dragons hatched from the pyre; Khal Drogo is dead; she leads a small khalasar remnant.
Season 1 established the game: succession lies, bastards, and winter. The realm fractures into multi-king war as S2 opens.
Arya escaped KL in chaos; Sansa remains hostage; Jon took the black.
Season 1 is the fall of honorable order: Ned's investigation of Jon Arryn's death exposes that Joffrey, Myrcella, and Tommen are Jaime and Cersei's children, not Robert's.
War begins in earnest: Robb wins early field victories; Jaime is captured by the North; Tywin maneuvers from Harrenhal direction.
Dany's arc transforms from abused exile to khaleesi with living weapons. Jorah Mormont advises her; Viserys is killed earlier for his abuse.
At the Wall, Lord Commander Mormont leads a great ranging plan; Ghost and Jon's bastard identity shape his bonds (Sam, Grenn, Pyp).
Season 1 establishes the lie of Joffrey's claim, Robert's death, and the realm's fracture.
Magic returns visibly via dragons and the dead. The Watch is undermanned and ignored.
Season bridge: everything above is end of Season 1. S02E01 ("The North Remembers") has not started.
Cutoff discipline: every fact above ends at S01E10. Do not import anything from S02E01 ("The North Remembers") or later.