For the most part, I am even using the correct definition of graphic novel, as distinct from other sequential art (comic books), because these were all conceived of as self-contained narratives.
Rebels by Brian Wood. It's a pretty fast story that covers a lot of historical material from the perspective of a normal person. There is a sequel about the main character's son as a shipbuilder in the War of 1812, and I might even say I liked it more than the first.
Wood has also written an excellent series of standalone comics about vikings called Northlanders. It's bloodier than Rebels, and harder to remember that it depicts history rather than fantasy, since its subject is so much more distant.
Robert Moses: The Master Builder of New York City by Pierre Christin does a good job of covering both the positive and negative aspects of Moses' legacy.
Logicomix, by Apostolos Doxiadis, which is about Bertrand Russell's development of set theory, the consequence of his monumental effort to prove that one plus one equals two. It is a metatextual Greek tragedy about the difficulty of obtaining even the smallest certainty in this world.
Crécy by Warren Ellis is about the famous battle in the Hundred Years War. It's short, and Ellis is a good writer. My recollection of it is that it was about how soldiers felt about the war, and that it gets a little blue.
Caravaggio by Milo Munera is also really good, and gives a great feeling not only of the artist's life, but of the world he inhabited. This is part of a planned multi-volume series, which to my knowledge has not materialized.
Flight of the Raven by Jean-Pierre Gibrat is also one of my favorite graphic novels ever. It's about some members of the French Resistance in occupied Paris smuggling people past the Gestapo. Pair it with the movie *Army of Shadows*.