This is another mixed-bag theme. On the one hand, in "For the Union Dead," Lowell commends the soldiers and Colonel Shaw for their great sacrifice in the Civil War. They fought extremely hard and gave the ultimate sacrifice: their lives. "But for what?" Lowell seems to wonder. Well, one answer might be: for the Republic, and that was a success. But they also fought for equality. These recently freed black men wanted to fight alongside the white Union soldiers as equals, and they did, but as Lowell surveys the current state of Boston, he still feels the "servility" that was supposed to die a century ago. He also sees that the memorials for the Civil War have blended into the background. Who will remember these guys for their sacrifices for our country? Well, at least for one, Robert Lowell will. It seems that this poem is trying to wake up the rest of the schmucks, and get them to recognize the same things.
In keeping with the "everything's bad, everything's sad" tone of the poem, Lowell thinks the great sacrifice of the soldiers was completely wasted, and that everyone has forgotten them. Bad times.
The poem shows—and admires—the continued sacrifice of African Americans, from the Civil War to the Civil Rights movement.