Participants in the Hundred Years War, the causes of the conflict between England and France.

The war was primarily attended by England and France. True, in certain periods of conflicts (there were 4 of them during 116 years) there were other participants.
On the side of England: Portugal, Navarre, Aquitaine, Burgandy, Brittany, Luxembourg, Flanders.
On the side of France: Aragon, Mallorca, Scotland, Bohemia, Castile, Genoa.
And some of the smaller ones.
The reason was that after the death of Philip IV the Fair, the Capetian line was interrupted. And King Edward III of England could claim the crown of France. And a representative of the outside branch of the Capetian Philip VI was crowned.