The thing to remember is that nations and nationalism are the centrepiece concept of politics today, but this is new.
Medieval politics was all about kings, lords and lordships. Not nations. National sentiments may have played roles, but secondary. Like the role race, class, ideology or whatnot today. Important, but nowhere near as central as nations.
The King of England wasn't very English much of the time.
The competing claims on england & france originate with Normans. They were if scandi origin, became powerful in France. They conquered England, Jerusalem, Cyprus, parts of Italy, etc. England became the house's important, long term procession... but they weren't English. They spoke french and claimed Viking ancestry.
Circa 1800 was a transitional period. Republican nationalism was exploding. Being a German house (Hanover) ruling England was becoming an issue. Royals started to adopt (previously derided) English folkishness. They raised their children in English, started speaking in a native accent, eating English foods and publicly participating in English activities.
You can still see this today, with British royals engaged in symbolic national "customs" like Scottish tartanry, Welsh language or whatever.
England wasn't claiming lordship over France. The king of England was. Up to 1800-ish, the king himself wasn't English. Not culturally and not by self-definition.
