I believe Robert held very high standards for his soldiers even though they were black. He treats them with dignity and equal respect as would be given to the soldiers who are white. He gives them a sense of humanity and dignity as if they belong there and are just as willing, competent, and capable of being good soldiers. By treating them with this respect they fight for a different reason other than because they have to, rather because they must meet the standards presented by their leader by proving they have all of these qualities.
This is very important because his soldiers treat him with more respect and care for him opposed to them fearing him and not feeling any compassion toward him. I believe Robert's principles of social justice are unlike any other military leader in the Civil War of his time towards the black soldiers. He put his career on the line for his soldiers so they may be treated as soldiers. He felt it was wrong to mistreat soldiers because of their skin color.
For example, one of the soldiers gathered up enough money to buy a new pair of combat boots and left camp without permission and was caught. Robert had to follow procedure by having him whipped in front of the group although he didn't want to. But when he found out the reason for the soldier taking the risk because he was in necessity for a new pair of boots and socks, he made his superior give his entire platoon standard uniforms, boots, and two pairs of socks. Robert defines leadership as treating all of his soldiers with equal respect and gives them all the opportunity to prove themselves as soldiers worthy of promotion. He feels he must give respect to his soldiers in order to receive it. At the beginning of the movie, the soldiers listened to and fought under Robert's command because they had to, and by the end of the movie, they fought for him because he stood up for them for them to earn respect from other soldiers in the army.
At the beginning of the movie, the soldiers are just fighting for the freedom of blacks that are still enslaved. By the end of the movie they were fighting for equality with the white soldiers of the north. The soldiers feel like the are fighting for their own well being and safety instead of for the unity of an entire country because they weren't treated as thought they were "real" soldiers. After Robert treated the soldiers with this higher level of dignity and respect, they fought for a greater cause. They were fighting for social justice and equality for blacks.
Not only for those blacks who are in the army, but for all of the black people in the United States. They also fought harder because of what was at stake if the north lost the Civil War. The soldiers define leadership as treating your soldiers as you would want to be treated if you were a soldier. They feel they should be treated as the capable soldiers that they are and not as puppets who are unable to make competent decisions, rather as soldiers who are ready to fight and die at a moment's notice for their country. At first they resist the leadership of Robert, until they realize that he holds high standards for their performance as soldiers on the battlefield and only wants them to gain respect of the other soldiers, both black and white. Then they embrace it and fight for their leader as well as for the abolishment of slavery, equal rights, and to be treated with a greater amount of dignity.
The soldiers act and feel like real soldiers. They feel the need to share this newfound dignity with the other black soldiers. They do not want to let go of the respect they have gained as soldiers from Robert and fought as hard as they could to retain that new respect.