The Final Battles of the Petersburg Campaign: Breaking the Backbone of the Rebellion by A. Wilson Greene.

The Petersburg Campaign was what finally did it.  After months of relentless conflict throughout 1864, the Confederate army led by General Ribert E. Lee holed up in the Virginia city of Petersburg as Lieutenant General Ulysses S. Grant's vastly superior forces lurked nearby.  The brutal fighting that took place around the city during 1864 and into 1865 decimated both armies as Grant used his man-power advantage to repeatedly smash the Confederate lines, a tactic that eventually resulted in the decisive breakthrough that ultimately doomed the Confederacy.  The breakthrough ad the events that led up to it are the subject of A. Wilson Greene's grondbreaking book, a significant revision of a much-praised work first published in 2000.