Tywin Lannister died without any other heir than Tyrion Lannister and his young wife Sansa, and rather than continue the mad fighting in Westeros Tyrion severed all ties and declared Casterly Rock neutral until a single King sat unquestioned on the Iron Throne. The fighting still continues, but House Lannister now takes in war orphans who are raised by Lady Sansa--it is this custom that first draws Daenerys Targaryen to Casterly Rock.

Tyrion knew, as he gazed up at the dark skinned Martell man that this was perhaps his only chance to spirit Sansa out of King's Landing and away from his father's greedy fingers. Tywin Lannister would have married the girl himself if he felt he could have gotten away with it, and so Tyrion knew his own marriage was no protection to Ned Stark's daughter whatsoever. "Invite her, demand her, steal her--whatever you choose, Prince Oberyn, choose it soon. Else my lady wife shall break into more pieces than the stars."