Factual error: During the battle scene the voiceover says that it is February 1915. The battle being portrayed is obviously the Second Battle of Ypres because it involves Canadian troops and it's the first time that gas was used in the war. The actual battle didn't take place until the end of April 1915.
Factual error: Prior to WW1, Colonel Ludlow picks up Samuel and Susannah at the train station in an all steel Model T Ford. This style of car did not come out until 1917. The correct car would have brass lights and radiator.
Factual error: The three Ludlow sons were leaving for England on October 14, 1914. When they were walking outside guiding their horses, the small trees in front of the house had green leaves. In Montana, Fall foliage typically begins by early - or mid-September. In most of the state, there should be peak Fall foliage (yellow/orange/red leaves) by early - to mid-October, not green leaves on the trees. Also, some time later when the sons were riding their horses through the field, the leaves were still green. (00:28:21 - 00:32:00)
Factual error: It has already been mentioned that, although the war scenes are set in early 1915, gas was not used until April of that year. There are further inaccuracies regarding this particular scene. The mask worn by the German cavalryman is not the sort of mask that was in use in 1915. It looks like a late WW1 or WW2 gas mask. Furthermore, since horses can also suffer from gas, a cavalry horse taking part in an attack in which gas was used would also be equipped with a gas mask. However, by early 1915, when both sides were dug into trenches, cavalry would not have been used anyway.
Answer: Very early in the story when one stab is narrating, he's kind of introducing everybody and makes a reference about Decker having "illegally" married an Indian woman, and there are several references to the fact that the father was not happy working for a government that was killing Indians and also went out of his way to make sure they were in no way discriminated against. I think it's possible that may be why they were looking for Decker and why Colonel went out of his way to hide his living there.
I believe Decker had been a bootlegger. That would be the reason why the O'Banions (sellers of booze themselves), were with the sheriff when they came looking for Decker at the Ludlow's ranch. And also, the reason why the O'Banions didn't want to say what Decker was wanted for because.it was their own personal vendetta concerning bootleg whiskey. Maybe they had reason to believe that he was still selling bootleg whiskey around those parts. Also, later in the movie, when Tristan returns home after 7 years, Decker says to him "There's good money in bootlegging if you know what you're doing." And, Decker says that with a huge smile. Like he definitely knew what he was talking about and could definitely give Tristan some pointers about being a bootlegger.
Alcohol wasn't illegal until well after World War 1. The initial scene with the O'Bannons takes place before the boys go off to war, and it's stated afterwards that Alfred voted for the Volstead Act making alcohol illegal.
Not sure about this. At the time the sheriff comes looking for Decker, it's roughly 1915, and liquor is not yet illegal.