Some thoughts on reading the book for the first time.
Influences from History:
King Robert Baratheon similar to Henry VIII; larger than life womaniser. Wife Anne Bolyn similar to Queen Cirsei Lannister, she was accused of having an affair with her brother and getting court jobs for her family.
Romans, praetorian guard choosing the new emperor. Valyrian might be ancient Greece or Rome
Ancient Egypt brother and sister marriages Pharos
Influences from Fiction:
"Ser" Tales of King Arthur knights of the round table
Khal Drogo of the Dothraki might be the desert from John Normans Gor series, perhaps Edgar Rice Burroughs Barsoom novels.
Dune house clan war
Zombies from many stories
Children of the forest = Elves
Then I read this from the author George R R Martin, he cites many influences.