The Battle of Brunanburh took place in 937, and is often referred to as the battle that made England. But there are a LOT of questions about that battle, including how it played out and where it took place.
Research:

Behind the Scenes Minis: Piece of Work
17:48

E. Virgil Neal: Hypnotist, Fraudster, Tycoon, Part 2
41:22

E. Virgil Neal: Hypnotist, Fraudster, Tycoon - Part 1
35:28