A Game of Thrones is set in the Seven Kingdoms of Westeros, a land reminiscent of Medieval Europe. In Westeros the seasons
last for years, sometimes decades, at a time.
Fifteen years prior to the novel, the Seven Kingdoms were torn apart by a civil war, known alternately as "Robert''s Rebellion" and the "War of the Usurper." Prince Rhaegar Targaryen kidnapped Lyanna Stark, arousing the ire of her family and of her betrothed, Lord Robert Baratheon (the war''s titular rebel). The Mad King, Aerys II Targaryen, had Lyanna''s father and eldest brother executed when they demanded her safe return. Her second brother, Eddard,
joined his boyhood friend Robert Baratheon and Jon Arryn, with whom
they had been fostered as children, in declaring war against the
Targaryens, securing the allegiances of
House Tully and House Arryn through a network of dynastic marriages (Lord Eddard to Catelyn Tully and Lord Jon Arryn to Lysa Tully). The powerful House Tyrell continued to support the King, but House Lannister and House Martell both dragged their feet due to insults against their houses by the King. The civil war climaxed with the Battle of the Trident,
when Prince Rhaegar was killed in battle by Robert Baratheon. The
Lannisters finally agreed to support King Aerys, but then brutally
turned against him, sacking the capital at King''s Landing. Jaime Lannister
of the Kingsguard executed King Aerys and House Lannister swore loyalty
to Robert Baratheon. The Tyrells and remaining royalists surrendered
and Robert Baratheon was declared King of the Seven Kingdoms.
Unfortunately, during the war, Lyanna Stark had died, apparently of
illness; Robert Baratheon instead married Cersei Lannister to cement the alliance. Despite Robert''s victory, the Mad King''s
youngest son Viserys and youngest daughter Daenerys were taken to safety across the sea by loyal retainers. After the war House Martell chose a path of isolation, since Prince Doran''s sister Elia (Prince Rhaegar''s wife) and her young children had been killed by Lannister armsmen during the storming of the capital.
Six years later King Robert proved his resolve by defeating a rebellion by Lord Balon Greyjoy of the Iron Islands. Balon''s two eldest sons were killed and his youngest son, Theon, was given to the care of Eddard Stark as a ward.