Why did Eleanor of Aquitaine bring Blanche of Castile to England, and for whom did she do it?
By the close of the twelfth century, relations between England and France had reached a very tense level, particularly over the fact that the kings of England, after Henry II's marriage to Eleanor of Aquitaine's in 1152 and his accession to the English throne in 1154, controlled more of France than the King of France himself. After Henry II's death and the death of his son, Richard I, his son John became King of England (r.1199-1216).
John, seeing an opportunity to alleviate tensions with the French king, Phillip II Augustus (r.1180-1220), proposed a marriage alliance between England and France. The answer came in the form of Blanche of Castile, the 11-year-old daughter of Alfonso VIII of Castile and Eleanor, the daughter of Henry II and Eleanor Aquitaine. As John's niece, a strategic marriage between Blanche and the future Louis VIII, the young son of Phillip II Augustus, would not only go a long way to easing tensions between England and France, but it also would bind the two kingdoms diplomatically, an important consideration for future matters of inheritance.
Eleanor of Aquitaine traveled to Castile to bring Blanche back to England. In 1200, the marriage between Blanche of Castile and Louis VIII was celebrated in England. While the marriage sought to improve relations between England and France, it only did so for a short time. Blanche soon proved a valuable ally for the French. Though she always showed concern for her uncle, she championed French attempts to assert its control in Europe, even against the English.