The more I look into both French and English/British history, the more I get the feeling that, over the time, there were several occasion on which France and the British Isles could have been united.
Here are some realistic examples I discovered :
1.Clavis Angliae Scenario
I name this one after a timeline that was posted on the board but was discontinued using the POD I will be talking about.
When John Lackland was excommunicated by the Church, king Philip II of France send his son Louis (the future King Louis VIII of France) to claim the English throne. At first, the Barons allied with Louis, but they ultimately choose to support John and Louis was defeated and forced back to France.
Had Louis vainquished John Lackland, he would have become King of England (as Lewis I) and, after the death of Philip II, King of France (as Louis VIII).
2.England winning the Hundred Years' War
If England had won the Hundred Years' War, then we would have the Kings of England as Kings of France.
This scenario could also happen if the French peers decided to have Edward III becoming king of France as Edouard I. This doesn't seem very likely though : the French did not like the idea of having a foreign prince ruling France.
3.Francis II of France living longer and having a son with Mary Stuart
If this were to happen, the son of Francis II and Mary Stuart would inherit France (from his father), Scotland (from his mother) and the rights to the throne of England (also from his mother) which he could claim after Elisabeth I's death.
An interesting scenario, but not a very likely one due to problems linked to Religion, problems in Scotland as well as Franco-English enemity.
4.Elisabeth I marrying a French prince and having a son
I recently read a book on the Tudors and discovered that, to secure an alliance between France and England, there were negotiations for Elisabeth to marry a French prince (on a proposition of Catherine de Medicis, Henri II of France's widow).
The first candidate was Henry of Anjou, the third son of Henri II and Catherine de Medicis and OTL Henri III of France. He said no.
She was then proposed Henry of Navarre (OTL Henri IV of France), but nothing was concluded as Henri III decided to say yes when he learned of this. Yet, when Elisabeth said she refused to hear mass with him, he refused again.
The last candidate was Catherine de Medicis and Henri II's youngest son, Hercules-Francis also known as Francis of Alençon. Francis came twice to England and Elisabeth seemed to like him. Yet, the thought of Elisabeth marrying a French prince was not popular in England and the wedding project was cancelled.
Of all those wedding possibilities, Hercules-Francis was the one that could have had the most chances to succeed : he was pro-reformation (he ultimately converted to Protestantism) and Elisabeth quite liked his manners. Yet, because of public opinion and because of he asked often Elisabeth for money (to help reformation in France and the Netherlands), she took a dislike in him and the wedding never happened.
Had Elisabeth one married one of the three French princes that were proposed to her and gave birth to a son, her son could have inherited the crown of France, no matter who she would have married (provided everything went OTL, of course).
Problems with this scenario : Elisabeth was nearing her fifties while the french princes were at least twenty years younger than her. The marriage would have shocked, but could have happened as it was considered acceptable for Kings. Yet, the chances of a son being born would have been low as women have a harder time in having childrens when they reach their fifties.
The other problem would be Religion : as time showed it, the French didn't want a Protestant King as it is the reason why Henri IV had to convert.
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I'll admit all those scenarios are not that likely and does not end with a stabilized Anglo-French of Franco-British Empire. Yet, it helps seeing how French and English history are that close from one another.
Thoughts?