Some useful links to learn more about the Civil War:
American Battlefield Trust
Battleground preservation with overview of battles and statistics
CivilWarTalk
Online community of Historians, Skirmishers, Re-enactors and Enthusiasts
Blue And Gray Education Society
Premier nonprofit organization for field studies & tours of battlefields & historic sites
Index - War of the Rebellion: Official Records of the Union and Confederate Armies
Cornell index- linked to actual documents in Hathitrust
Library of Congress Civil War Maps
High resolution, downloadable maps of the Civil War
Battles of the American Civil War
A chronological tour and interactive map of decisive Civil War battles
CWRT Congress
Information on all other Civil War Round Table activities worldwide
Inland Empire Civil War Round Table
An active Civil War Round Table in Southern California
Better Soldiers and Sailor's Database
Replaces the obsolete National Park Service Civil War database
Civil War Photo Collection
Library of Congress photography and drawing collection related to the Civil War
History.net Civil War
On-line magazine of topics regarding the Civil War
Harper's Weekly
A reference to available digitized Harper's Weekly
Chronicling America
Library of Congress’s free searchable online newspaper collection.
National Park Service
Civil War online resource page
U.S. Archives- Military Records
General research materials