The title refers to the biblical fall from innocence. In Sweden, however, the title was translated as "Höstlegender" meaning Legends of the Fall (the season, as in autumn). Similarly, in South Korea, the title was "Gaeul-ui jeonseol" interpreting "the fall" as the autumn season. The same in France, where it was named "Légendes d'automne" also in Romania, named "Legendele toamnei".
The brothers enlisted in the Canadian Army, and appear to have served in the 10th Battalion Canadian Expeditionary Force, by the badges on their uniforms. The 10th Battalion was formed from the 103rd Regiment (Calgary Rifles), which was later known as The Calgary Highlanders. Several soldier extras were current members of the Calgary Highlanders.
The book from which Colonel Ludlow is reading the night the boys announce they're going to war is the short story "Rikki-Tikki-Tavi" by Rudyard Kipling in "The Jungle Book", volume two. Rudyard Kipling's son John served in World War I, and was killed in action. My Boy Jack (2007) was based on these events.
The trivia items below may give away important plot points.
When shooting the scene where Isabelle Two (Karina Lombard) is shot, and Tristan (Brad Pitt) gets beaten up by the policeman, the actor playing the policeman accidentally hit Brad on the head with the baton, giving him a black eye. Shortly after that, they shot the tennis scene that's near the beginning, and Brad still had his black eye. They had to make up a couple of lines about his "shiner" to explain it.
The final line, "It was a good death", was also used in another Edward Zwick directed movie, The Last Samurai (2003), when Captain Algren (Tom Cruise) finds out that he killed Katsumoto's brother-in-law, Katsumoto (Ken Wantanabe) replies, "It was a good death".
Brad Pitt claimed that he underwent make-up tests to play Tristan as an old man in the epilogue, but the results were unconvincing. Old Tristan is played by Doug Seus, Bart the Bear's trainer, the only man who could safely wrestle with Bart on-camera.
A foreshadowing of the progression of the storyline happened, when a young Isabel Two told Sussanah, she "was going to marry Tristan". Tristan married Isabel Two when she was older, and had two children.