The Dragon Star
The vast majority of background info for the world is historical information that can be found online. The best general Wikipedia articles are a summary of the 12th century, a summary of the 1130s, and 1137 in specific. For specific topics, there’s the Papal Schism, the Renaissance of the 12th Century, The Anarchy in England, and the Crusader States.
Also available is a map of Europe prior to the event. (Post-event maps to come soon.)