Library of Congress
Loc: Civil War and Reconstruction
This site from the Library of Congress provides overviews of the South and North during the Civil War include soldiers' stories from both sides. There are primary documents on these topics as well as Freedmen and the Reconstruction.
Kidport
Kidport Reference Library: The Civil War
Here is a summary of the factors that led to the Civil War. You can also link to pages with photos on battles, forts, communication, hospitals, and more.