Short answers, pulled from the story.
The Norman Conquest reshaped England's legal landscape in 1066 by replacing fragmented local courts with a unified royal system. Before this event, shires and hundreds operated their own folk courts while urban boroughs maintained separate jurisdictions.
Common law emerged as a recorded body of decisions by the thirteenth century from judges returning to London to discuss rulings. The Year Books first appeared in 1268 as compilations of medieval court cases that documented developing doctrines.
Thomas Bracton wrote On the Laws and Customs of England during this period to explain emerging principles. This work helped document the transition from itinerant justices resolving disputes based on local customs to a formalized system.
Erie Railroad v Tompkins decided in 1938 overturned Swift v Tyson which had previously allowed federal courts to create general common law rules applicable within states. Federal courts limited general common law creation after this decision restricting jurisdiction to admiralty and constitutionally specified domains.
The Supreme Court of the United Kingdom gained power to unify criminal law decisions across England Wales and Northern Ireland starting in 2009. Before that date the House of Lords held this authority through its Practice Statement of 1966.