Old Kingdom of Great Britain

The Old Kingdom of Great Britain (so named to differentiate it from the later state of the same name) was a state that existed hundreds of years before the Century War. It was formed through the acts of union that united the kingdoms of England and Scotland under one government. Wales and Cornwall, two other previously independent countries, were already under English rule at this time.
A century after it's formation, Great Britain merged with Ireland to create the United Kingdom of Great Britain and Ireland. The name Great Britain was still used colloquially to refer to the United Kingdom long after.