I've always been intrigued by soldiers in the 18th/19th century. The warfare in that period pretty much consists of standing in line facing the enemy taking shots at each other. Now warfare is always brutal and scary but this period in history must have been the most scary for sure. In earlier eras you had shields and armor, in later periods you take cover in trenches or behind buildings. (A thing or two can be said about charging into machine gun fire in trench warfare though, jesus christ!)
It would be fascinating to see a film dealing with the training of these soldiers, the psychological impact etc. Can you imagine how terrifying it must have been when after a volley shot by your opponents, you see dozens of men next to you drop down and then in a split second your company either runs and loses and gets slaughtered nonetheless by the cavalry or they stand ground continuing to play basically Russian roulette.
What was happening in these soldiers minds, how did they train this giant game of chicken, how did higher ups punish undisciplined soldiers, was there alcohol involved before battle? What was the mood of the soldiers themselves, did they realize what they were getting into?
It could be a completely fictional movie, with fictional countries so it doesn't turn political or personal. With the focus on the soldiers not the conflict. It would also give insight in why exactly this was the ideal way to wage war back then. It looks silly to modern people, I've seen people comment that back then people were just dumb but it's a ridiculous comment. There is always a reason why things are done the way they are done, if this was the most effective way of fighting then I think it is worth making a story around it.