In order to correctly discuss this period we must have some background. On the 14th of October 1066 the Battle of Hastings ended forever the Anglo-Saxon rule of the island which would be called England. William the Bastard

For the immediate time William and his successors were more involved in consolidating their hold on England through a period of conquest, and then of civil wars. The Anglo-Normans were replaced by the Angevins whose hold on England was secure, and they also acquired additional lands in western France, Maine, Potiou, Anjou, Touraine, Gascony, Saintonge, and Aquitaine. By this time their holdings included more territory than the French King yet still they continued to be vassals of the French King. This was, of course, a cause for continual friction. (Please note that during this time the Second, Third and part of the Fourth Cruasdes were being called. This acted as somewhat of a relief mechanism for unruly military men.) There were, however, three successive wars in which the French regained some of the lands. These were the Conquest of Normandy (1214), the Saintonge War (1242), and the War of Saint-Sardos (1324). These conflicts had the effect of loosening the grip of the Agevins on France but also of creating an atmosphere for the desire for revenge and the regaining of the ancestral homeland. At this period the English noble classes still spoke French exclusively and the memories of their great-grandparents still existed.
In 1328 the Capitian dynasty ended with the death of Charles IV. His father Philip IV had been the Grand-son of

The English did not care for this one bit. The loss infuriated the English nobles who viewed the loss of lands as mismanagement. In 1327 Edward was assassinated and his wife Isabella the daughter of the French king Philip IV and sister of the current French King Charles IV de facto ruled England for her son Edward III

As has been a feature in medieval warfare much time was spent in negotiation between ountries. Especially France and England, many of whose nobles held lands in both France and England. It was important for the nobles to at once been seen as supporting their lieg and also to look after their own interests, in lands and income. This "fence sitting" will have a great bearing on the alliances struck up and changed during the Hundred Years war.
A word about the languages. When one speaks of the French in the context of the Hundred Years War, it is only by the use of a more of less common language that they can be grouped. To most of those who lived during the period in what would become France at a later date, France was only the territory surrounding Paris, Capital of the Valois. One might be Champagnois, Normandois, Poitevin, Breton etc. and that is how they thought of themselves. Most of the provences were duchies whose nobles held their lands in fief from the King to whom they would pay homage, including monies and were required, but did not always come, to the aid of the King in times of war. Much of the language was French but there were and are still today patois, dialects, much like the French spoken in France today compared with Quebecois French, (my daughter never fails to comment on my quaint Quebecois accent), or Occitan spoken then and still in Provence, Langudoc, and parts of northern Italy. Again remember that until just at the end of the War both sides spoke French in daily use.
Thus at the death of Charles IV the stage was set for the opening actions of the Hundred Years War. It would be Valois for France versus the Plantagenet for England.
Below is the family tree which will introduce the next part.
