"Northmen" who we sometimes call Vikings today somewhat incorrectly, started spreading out circa 850 AD and one group headed by a fellow named Rollo settled in the area of France we now call "Normandy", oddly enough. Northmen/Danes had raided Paris several times, and Rollo had control of the Seine River, and in return for keeping the hords out of Paris, the French King gave him the land and a dukedom. His grandson, born in Falaise with the French name Guillaume, had a claim to the English crown, which he thought was taken from him, so he assembled an army and ships and crossed the "French Channel" and defeated Harold of England at the Battle of Hastings in 1066 and became King of England and Duke of France, a situation which lead to hundreds of years of war. It also greatly impacted our language.
Previously, the Britons were pushed out of England by invading Saxons and Angles into a peninsula called Wales today, and some of them fled by ship to another area of France we now call Brittany, where the local Breton language has some overlap with modern English, and their flag looks a bit like ours.
So, we are German, Danish, French, Norwegian, Irish, Roman, and whatever else as is the English language.