In 1066, Normans from France invaded and conquered England, which until then had been under Saxon rule. By a series of royal marriages, it worked out that one branch of the French royal family ruled at home, while their kinsmen ruled England.
When the French royal line in France failed, King Edward III of England claimed to be heir to the French throne. The French nobles would not stand for this, and crowned their own man as king.
The English had political troubles in Scotland, which the French did their best to inflame. The French had their own troubles in Flanders (part of modern Belgium), and the English incited rebellion there. So, both countries faced hostile neighbors on two fronts.
In 1337, Edward III went to Ghent, the capitol of Flanders and the largest city in Europe at the time. There, he had himself crowned king of France, and proceeded to fight his way back to the coast. This ignited the Hundred Years War.
The character I portray, Charles Fleming, is a Flemish partisan from Ghent who fought with the English in Edward's great naval victory at Sluis in 1340. He went on to march and fight with them for six more years, finally taking part in the Battle of Crecy in 1346.