The knight that appears in young Vivienne's visions carries a familiar sword: Anduril, Aragorn's sword from The Lord of the Rings: The Return of the King (2003), which was gifted to Viggo Mortensen by Peter Jackson at the end of filming.
Viggo Mortensen did not intend to act in the film. "Late in the game", the actor who had originally been cast as Holger left to work on a different project. Vicky Krieps suggested he take the role himself.
On casting Vicky Krieps, Viggo Mortensen said, "I thought she would be great as this character. Very quiet but with a particular point of view. I needed someone I could believe was from the 19th century, and I don't believe that about all actresses I see for various reasons."
Vivienne makes a living selling flowers, as did writer-director Viggo Mortensen when he was a young man living in Denmark.
The war in Denmark which Olsen fought in was presumably the First Schleswig War (1848-1851) in which Denmark fought the German Federation for control of the regions of Schleswig-Holstein. Denmark was indeed victorious.
Ironically, whilst Olsen is fighting in the American Civil War, the Second Schleswig War was fought, after which Denmark was obliged to cede the disputed regions.
Ironically, whilst Olsen is fighting in the American Civil War, the Second Schleswig War was fought, after which Denmark was obliged to cede the disputed regions.