I would think the standard work on the Civil War, and easily the best I've read, is
Shelby Foote's The Civil War: A Narrative (ebooks, full set). It deals with the entire war and its causes in great detail over three hefty volumes, without ever becoming dry or boring.
Vol 1: Fort Sumter to Perryville (ebook)
Vol 2: Fredericksburg to Meridian (ebook)
Vol 3: Red River to Appomattox (hardcover)