The Battle of Little Bighorn took place on this date in 1876. In the Wikipedia article that describes the battle, possible reasons for Custer’s defeat are given (condensed from the original, earlier edition of entry):
Unfortunately (for Custer and his troops), this aggressive action was deeply flawed as a military tactic. First, Custer did not have adequate information (or did not believe it) on the size of the Lakota/Cheyenne encampment. … Second, Custer did not know the terrain from which he would attempt his attack. … Third, Custer set his regiment up for “defeat in detail” by dividing it into three smaller battle units (the troops assigned to the pack train were a necessary part of any battle plan), that could not quickly support each other….
Do you think that these are valid reasons for the defeat, or do you think that they lie in another direction?