But he was fighting for the dignity of man and in that way he was fighting for himself. If men were equal in America, all these former Poles and English and Czechs and blacks, then they were equal everywhere, and there was really no such thing as a foreigner; there were only free men and slaves. And so it was not even patriotism but a new faith. The Frenchman may fight for France, but the American fights for mankind, for freedom; for the people, not the land. (1.2.119)
Chamberlain sees the Union cause as something more than just nationalism. In his view, the Union is defending America, sure—but they're also defending humanity as a whole. They're putting to death the idea that all men are not created equal, and they're trying to turn the Declaration of Independence's promise of equality and liberty into a reality.
"Most of us never saw a black man back home. We think on that, too. But freedom… is not just a word." (1.2.138)
Speaking to his troops—and trying to convince the soldiers who had refused to fight to take up arms again—Chamberlain acknowledges that they might never have seen the people they're fighting to free from slavery. But he insists that the cause is important nevertheless, because freedom is inherently important.
"Well, Jim Kemper kept needling our English friend about why they didn't come and join in with us, it being in their interest and all, and the Englishman said that it was a very touchy subject, since most Englishmen figured the war was all about, ah, slavery, and then old Kemper got a bit outraged and had to explain to him how wrong he was, and Sorrel had some others joined in, but no harm done." (1.4.173)
The British Government didn't know which side to support during the war. In fact, it was leaning towards supporting the South, because Britain wanted to keep trading for the cotton produced there. However, the British had already abolished slavery—making supporting a slave-holding state kind of a sensitive issue.
But he felt it again: a flutter of unmistakable revulsion. Fat lips, brute jaw, red-veined eyeballs. Chamberlain stood up. He had not expected this feeling. He had not even known this feeling was there. He remembered suddenly a conversation with a Southerner a long time ago, before the war, a Baptist minister. White complacent face, sense of bland enormous superiority: my dear man, you have to live among them, you simply don't understand. (3.2.33)
Chamberlain has a moment of crazy racist panic. Unexpectedly, he feels repulsed when he sees a runaway slave and momentarily wonders if the Southerners are right. This won't last long, but it does raise another issue—slavery is one thing, but racism is another. It's easier to abolish slavery than to abolish racism, and even good men like Chamberlain have to check themselves sometimes and realize that they have biases and fears, too.
He backed off. He stared at the palm of his own hand. A matter of thin skin. A matter of color. The reaction is instinctive. Any alien thing. And yet Chamberlain was ashamed; he had not known it was there. He thought: If I feel this way, even I, an educated man… what was in God's mind? (3.2.43)
Chamberlain feels ashamed. He recognizes that, despite his supposedly enlightened views, even he can fall prey to knee-jerk racial judgments and reactions.
He felt a slow deep flow of sympathy. To be alien and alone, among white lords and glittering machines, uprooted by brute force and threat of death from the familiar earth of what he did not even know was Africa, to be shipped in black stinking darkness across an ocean he had not dreamed existed, forced then to work on alien soil, strange beyond belief, by men with guns whose words he could not even comprehend. What could the black man know of what was happening? Chamberlain tried to imagine it. He had seen ignorance, but this was more than that. What could this man know of borders and states' rights and the Constitution and Dred Scott? What did he know of the war? And yet he was truly what it was all about. It simplified to that. Seen in the flesh, the cause of the war was brutally clear. (3.2.48)
As Chamberlain thinks more about the issue, his initial lack of sympathy for the runaway slave morphs into real sympathy. He also muses on the irony that, since the slaves weren't allowed to learn or keep up with current events or anything like that, the people he's fighting to free aren't aware of all the issues surrounding the struggle. Also, even though Chamberlain knows he has some racist tendencies, he decides to work through them in order to try overcome them.
He started to move off, and then he turned, and to the black face looking up, to the red eyes, he looked down and bowed slightly, touching his cap. "Goodbye, friend. Good luck. God bless you." (3.2.63)
In this little mini-drama within the story, Chamberlain comes to respect the runaway slave, acknowledging him as a human equal. He gives him this touching farewell.
"I have reservations, I will admit. As many a man does. As you well know. This is not a thing to be ashamed of. But the thing is, you cannot judge a race. Any man who judges by the group is a peawit. You take men one at a time, and I've seen a few blacks that earned my respect. A few. Not many, but a few." (3.2.94)
Kilrain doesn't seem like a serious abolitionist or anti-slavery man, but he does think the whole idea of judging an individual by the group he belongs to is nonsense. The real reason Kilrain is fighting is that he wants to end the Southern aristocracy and let people be treated based on their own merits instead of based on who their ancestors were.
"Of course, I didn't know that many. But those I knew… well, you looked in the eye and there was a man. There was the divine spark, as my mother used to say. That was all there was to it… all there is to it." (3.2.94)
Unlike Kilrain, Chamberlain has more of the real anti-slavery spirit. Since Chamberlain's fairly religious, he believes that God created everyone to be equal.
"I tried to point out that a man is not a horse, and he replied, very patiently, that that was the thing I did not understand, that a N**** was not a man. Then I left the room." (3.2.102)
Chamberlain remembers arguing with a visiting Southerner back in Maine. The Southerner insists that African Americans aren't really human, which disgusts Chamberlain. It doesn't seem compatible with the idea that all human beings possess a "divine spark," since they were created by the same God.
"I don't really understand it. Never have. The more I think on it the more it horrifies me. How can they look in the eyes of a man and make a slave of him and then quote the Bible? But then right after that, after I left the room, the other one came to see me, the professor. I could see he was concerned, and I respected him, and he apologized for having offended me in my own home." (3.2.103)
Even though Chamberlain finds the Southerner's views on slavery and race abhorrent, the Southerner still tries to be polite. It's part of the difficulty of fighting the war: the South has a conception of morality and manners while still totally disavowing human equality and treating the slaves horribly.
The war was about slavery, all right. That was not why Longstreet fought but that was what the war was about, and there was no point in talking about it, never had been. (3.5.197)
Longstreet admits to himself that the idea that the South is fighting for states' rights is hogwash. In his view, they may really believe that, but they're fooling themselves. But what is Longstreet fighting for? Is it just that he feels obliged to defend the place he's from?
"Well, then, I don't care how much political fast-talking you hear, that's what it's all about and that's what them fellers died for, and I tell you, Lawrence, I don't understand it at all." (4.6.17)
By the end of the story, Joshua Chamberlain and his brother, Tom, have reached some moral clarity about the war: they see that it was caused by slavery. Of course, Chamberlain basically thought this before—but, now, after Gettysburg, it seems totally obvious to him.