It's about being trapped

That's very good insight to this film and I thank you for bringing it up. I have never read the book but I have been watching this movie for about twenty years. I just watched the directors cut for maybe the third time, I am glad I saw it because the theatrical version never mentions Longstreet's children dying of scarlet fever. I also have always liked how this film tells both sides of the story. Most of the old John Wayne type Civil War movies never show any character development on the Confederate side.

Interesting take.

I've always seen it as being about motivations.... about how all those various people all ended up in Gettysburg in July 1863 and why they did what they did once there.

Lee was as American as they came in 1860: Son of a revolutionary war hero, army officer and war hero himself (in Mexico) and married to a grand daughter of Martha Washington. Although he owned slaves, he had no strong feelings about the practice. However, he considered himself a Virginian before he considered himself an American and thus fought for the south. By 1863, he was a sick man, feeling his mortality and seeing himself and his army as the South's only hope. Unsure of how much longer his health would allow campaigning and unsure if his underlings could win the war without him, he took desperate chances at Gettysburg hoping to win the war in one battle.... and failed.

Joshua Chamberlain, on the other hand, was a New Englander, and he saw the war as a crusade intended to right a great wrong, and he had no qualms about dying for a cause like that. He'd also spent his life before (and after) the war in a classroom. This was his one and only chance to do something amazing... As an individual and as a representative of
humanity.

The rest have their own motivations that often go well beyond the fight over slavery or freedom... states rights or federal power.... rural or industrial. Ewell had always had a strict and strong commander over him until Gettysburg and he shrunk under the pressure of decisions. Pickett was an amiable sort to whom life and even war was a bit of a lark until he had to watch his division die on the fields of Gettysburg. Buford was an old soldier who did what was best for the army that employed him, politics (personal or otherwise) be damned. Etc, etc, etc.