Two months after marching through Boston, half the regiment was dead;
Heads up: time shift! Lowell goes back to describing the Civil War and the fate of the 54th infantry.
So, after marching south for two months, the regiment had lost half its members—that's a lot.
The soldiers sacrificed their lives. Now we're beginning to understand the title and the epigraph of the poem. They give up all, including their lives, for the Republic.
at the dedication, William James could almost hear the bronze N****es breathe.
Time jump again. What, does this speaker have a Delorean or something? Lowell skips past the end of the Civil War to the dedication of the memorial.
The dedication Lowell is talking about here is the unveiling of the memorial. Usually there is a ceremony with a speaker to commemorate the dead.
William James, a big-time philosopher from Boston, gave the dedication speech.
To say he could almost hear the bronze soldiers breathe might mean a few things: that they looked very real, and/or that he was so moved by their courage, and the sacrifice was so fresh in his mind, that they seemed very real to him.