Gettysburg Staff Ride - Background, insights, cause and objectives. 

Every man had his own motivations, but generally speaking...early on, there were less men motivated by abolition, and more motivated by preserving the Union. As time went on and northern men got to see the results of slavery up close and personal - and as black men joined the army and proved themselves on the battlefield - abolition became a stronger and stronger motivation. Here's an anecdote that demonstrates the shift: “We found the two men handcuffed and tied with a log chain, in the cane break, and the other lot in a swamp where the water was half-knee deep in the shallow places. They had been in this condition for forty-eight hours without fire or food. They were the most miserable looking lot I ever saw. They scarcely had any clothing at all, ragged, dirty, and barefooted; it had snowed that morning and that night it froze hard. So I think that you will not blame us for taking pity on them. I wouldn't see a dog treated so. It made abolitionists out of Wils Payne and several other Democrats.” - Captain Jacob Ritner, Co. B, 25th Iowa, quoted in Iowa and the Civil War Volume 2, Kenneth L. Lyfrogt