Whoever told you there was no England or France back then is wrong. Both countries existed as nation states, even though their territorial reach was not the same as it is now.As an aside, I've been taken to task by another of members for framing the Hundred Years War as being fought by the "English," against the "French." He said there was no England or France back then and that was a terribly unsuitable way to describe the conflict. It was better he said, to say the war was fought between the house of Valois and the house of Plantagenet. Imo, that, too is an oversimplification. Ergo, imo, some generalization is helpful in matters like this and "England vs France," is an acceptable way to frame the war. Thoughts?
That said, characterising the Hundred Years' war as a dynastic struggle between two rival houses seems right to me. Although we are conditioned to think of 'England' and 'France' as we understand those terms today, it really wasn't the same back then. With the exceptions of John and (I think) Stephen, who were probably the two most hated kings of medieval England, the kings of England up to the end of the War generally spent far more time in France than they did in England. They spoke French and operated in a world in which France was the prize. Anyone who has ever been to the Perigord region of France can see the evidence in the enormous castles and the fortified bastide towns that face each other across rivers such as the Dordogne.
This doesn't mean (as one poster suggested) that had 'England' won, England would later have had to fight a war of independence agaist France. Such a hypothesis assumes that what we have now in terms of two neighbouring nation states was inevitably going to be the end result. That is a totally unwarranted conclusion. Had 'England' won and had the centre of power remained in France, we might (or might not) now be living in something like the Grand Nord region of France comprising the existing French departments in and around Picardy and the Pas De Calais together with departments with names like Trans-Manche, Severn et Trente, Vielle Bretagne, Bas-Angleterre and Haut-Angleterre. In keeping with historical precedent, it may well be that the inhabitants of Trans-Manche and Bas-Angleterre (being the lowland regions of England) had much more in common with their cousins across the Channel than those of us living in the northern uplands of Haut-Angleterre (aka la Pays de Pluie). English speech - or the hybridised pidgin of English and French known as le Langue Du Nord - may only have been spoken in this area, with multilingual road signs and our own flag showing two whippets rampant being pretty much the expression of our independence from Paris, which we'd undoubtedly despise as much as we currently despise London!