I think one of the best exchanges in the whole film is when Trip (Denzel Washington) talks informally with Colonel Robert Shaw (Matthew Broderick) by the lakeside camp before the Battle of Fort Wagner.
Trip said, "Why are we fighting this war? Ain't nobody going to win."
Shaw said, "Well you won't get anything if we lose."
That's so true and completely encompassing of the situation they faced.
Ignore some of the political reasons the Republicans (then controlling the Union) wanted to win the war.
It was the idealists who wanted to free the slaves - idealists like Col. Shaw. And it was all the slaves who wanted their families to be free (like Sgt. Rollins - Morgan Freeman).
As the movie clearly showed, racism would persist and many didn't care if it did. At this stage, blacks just wanted to fight for their freedom. And they had no where to go. They were many generations removed from being African. Once they had their freedom, they would just be unwanted free people in a land they had to adapt to living in on their own. Maybe characters like Thomas wanted to also have a right to vote, own land, etc. but others just wanted to be free and couldn't even conceive of a Civil Rights movement, let alone Barack Obama, 150 years later.
But Trip was right too: "Aint nobody going to win." In a way, he was right. The real victory for most people didn't come after the Union was held together. The slaves were free as a strategic consequence really - a victory for black people I'd say. But many white soldiers fought because they needed work or to feel like they weren't cowards. The Irish brigades were filled with men who's only concern was to escape starvation.
Indeed, I don't think we've yet seen the complete victory of the Civil War realized. Barack Obama is another step towards that - and we are closer than we ever were before (those of us who are idealists), but the Civil War is not won yet (in terms of equality issues). In terms of the supercedence of the Union over States' Rights, then yes, I'd say 1865 settled the issue. Those fighting the war didn't seek that particular victory though.
I wonder if Robert and Trip thought of any of this themselves, or if Robert saw an 'effed world" which didn't hold enough meaning for him to remain in, versus charging up that last hill to Fort Wagner?