This article attempts to reveal the complex relation between American idealism in the past and the spiritual deterioration of its present day Boston by reading “For the Union Dead.” Throughout the poem, the highly ideal attitude of Colonel Shaw of the Massachusettes 54th is contrasted with the deteriorated morality of present day Boston. The human values Shaw tried to keep alive by even throwing away his life seem to have died in Boston. Apparently, American history appears to have proceeded in the opposite direction from the ideals in the past represented by Shaw. But as the poem`s multi-layered meaning is unfolded, the hidden motives of Shaw`s determined idealism are brought to light. His idealism is revealed to have been stained by death impulses and violence. His own uncompromising rigidity when he led the black soldiers to their death, the bombing of Hiroshima, political anxiety and fear of the 1960s, and the discrimination still spread over the country all serve to prove Lowell`s critical stance about Shaw`s hidden motives. Thus, the complex relationship-succession and betrayal-between idealism in the past and the present reality, as well as the ambivalent characteristics of American idealism itself are revealed by the close reading of “For the Union Dead,” a poem seemingly celebrating Colonel Shaw.