For browsing purposes, some relevant Library of Congress call numbers for the United States Civil War are:
E456-655 Civil War period, 1861-1865
E456-459 Lincoln's administrations, 1861-April 15, 1865
E461-655 The Civil War, 1861-1865
E482-489 Confederate States of America
E491-586 Armies. Troops
E591-600 Naval history
E668 Reconstruction (U.S. history, 1865-1877)
When searching for books the main Library of Congress (LC) subject heading for the United States Civil War is:
This heading is divided by LC sub-headings. Some sub-headings you may want to try to narrow your search further are:
Any of the above LC subject headings can be copied directly into the Regent Library Catalog, and other Regent databases, and searched by Keyword or Subject.