The Last Great Battle of the American West (2009).
Lieutenant Colonel George Armstrong Custer (his superior officer was General Alfred Terry) only had about 660 men (he was part of a single column), including only 31 officers, 578 enlisted men, and 45 or so scouts/guides (most of them Natives). Each soldier had the single-shot breech-loading 1873 Springfield carbine, which had an Achilles Heel - the copper cartridges would heat and jam upon firing, and had to be pried loose, usually with a knife. Other than that, the Springfield was a relatively cheap and reliable carbine with stopping power (each soldier had 100 rounds of ammunition). Also, there was the Colt .45 sidearm (24 - 74 rounds issued), and the pack mules carried 26,000 more carbine rounds.
Custer saw many diverging trails, but the Native scouts knew that they were actually CONVERGING trails, instead. Custer (and the other officers in the 3 columns) was too obsessed with the belief that the Natives were in the process of scattering, like cowards, in their view; there was a collective sense among the officers that if they took too long to engage, they would miss their chance at a decisive victory since the Natives would scatter and disappear. Custer calculated that he was only one day's march from much-desired and much-delayed glory . . . he ordered his regiment to follow the trail leading to the lower reaches of the Little Bighorn River.
Benteen was ordered to move toward the bluffs, deal with whatever he came across, and then rejoin Custer's right wing, all the while tending to the pack train. Custer expected Benteen to return fairly soon (as in an hour or two) if he didn't find any Native warriors. Benteen had gone from leading the regiment on the initial advance to being given a secondary mission; to him, it was the playground football equivalent of being told to go long, and the QB would fake a pass towards him. Benteen firmly believed that Custer was getting his long-delayed revenge against him for voicing concerns about Custer's decision-making at the Washita in 1868.
Custer had about 220 men; he not only didn't have enough enlisted men, but he was short officers as well. Although the officers he did have at this point were inexperienced, they were accepted as members of the "Custer Family" (a.k.a. Custer's "Circle of Trust"; officers such as Reno and Benteen hated Custer). Custer knew Reno was under attack, and he changed his mind about directly supporting him; Custer decided to attack the Native warriors from the flank . . . the perceived benefit to Custer was that he could secure even more glory.
However, Custer never sent a messenger to let Reno know of his change in tactics. Back with Reno's wing, the major gave the order to attack, but his speech was slurred . . . he had been drinking whisky from his flask (Reno was an alcoholic).
Reno's 100+ men dismounted about half-a-mile from the nearest teepees; they were spread out across 250 yards, and Native warriors were advancing towards their skirmish line. When Custer saw Reno and his men retreat to the timbers and scrub by the Little Bighorn, he decided it was time to make his glorious attack.
Reno then gave his "Come With Me" order, but didn't arrange for any rearguard action, which was standard military procedure, and more-than-warranted in this situation. To the pursuing Native warriors, it seemed like a '"Buffalo Chase"; Reno lost about half his men on the badly organized-and-led retreat to the bluffs across the Little Bighorn River.
As Custer surveyed his situation, he saw a dust cloud in the distance; he believed that it was Captain Benteen's wing, and that he was no more than 30 miles away. Custer thought that victory was still possible with an attack, not so with a retreat. So Custer once again (for the third time overall) split his troops (this time, he divided his battalion) - his goal was to help Reno, and stay on the offensive . . .
A relevant segment from "Son of the Morning Star" (1991 TV Miniseries)
a) Benteen's frustration at being "sent long"
b) Reno's initial attack on the village . . . notice how there is a bugler . . . inaccurate!
c) Reno stops his charge and forms a skirmish line; Custer goes for glory
d) Reno orders a retreat to the timbers/scrub by the LBH
e) Custer makes his flanking move on the village; the village gets more organized