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:

SYMHC Classics: COINTELPRO 1
39:12

Behind the Scenes Minis: It's Not Unprecedented
16:46

The Rendition of Anthony Burns, Part 2
43:32