In the movie "War Horse" the Regiment Cavalry Commander (Benedict Cumberbatch) advised his subordinates "from Waterloo to Omdurman, to Pickett's Charge to the Battle of Mars-la Tour, the first attack is decisive".
What lessons or insight did Europeans see from this battle or subsequent battles from the American Civil War?
More can always be said, but this AMA with /u/MSomervi_UK should prove to be of interest for you, at least as regards the UK!