The Hundred Years' War was fought between mainly France and England during the late Middle Ages from 1337 to 1453. It was a war that defined an entire period in Western History and lay the foundations for modern Western European society and culture. It was an era full of distaster, disease, and great political conflicts and social upheaval, but also with building new, religious miracle and chivalry unparrallelled. It was an exciting, tragic, yet hopeful era that this Civilization 5 mod depicts.
The addition of City States in Civ5 is used to some extent in The Hundred Years' War too. Here we see Avignon, the interim seat of the Holy Father, the Pope himself.