Four Years Under Marse Robert Book

It cannot be overstated just how unprepared both sides were, materially, physically, psychologically, for the war that fell upon them in the late spring of 1861. In this the second volume of Time Life's magnum opus: The Civil War, William C. Davis does yet another excellent job of concisely narrating the opening phases of the war.
Both sides were convinced it would be an easy, short fight, and both sides eagerly volunteered in droves to join the freshly raised volunteer units.
As Davis points out, the North had the strategic advantage in terms of initiative. The North could call the shots, decide where and how to invade the Confederacy, and when. The North had far and away a stronger economic and logistical base, and had access to technology the South could only procure from Europe. And even then it would have to evade the US Navy's coastal blockade.
However, the South had the advantage of a more youthful, and energetic, officer corps, had a massive territory (larger than continental Europe) with which to maneuver in, and ironically, her dearth of extraneous logistics meant that her smaller field armies could move more rapidly, and retain superior operational and strategic mobility, over and above that of her heavier Federal opponents. And being the defender, her men, wether linked to slavery and secession directly or not, would fight like tigers for their homeland against an invading force.
By June of 1861 the time of mustering came to a close and the Federal forces on the Confederate periphery began to advance inland.
Davis narrates the small scale encounter at Big Bethel on the Virginia Peninsula, a rebuke to Federal forces that did much to toughen Rebel resolve, as well as alert the Yankees to the difficulties of operating in the region. Lessons that were learned and used to hone later, grander, moves on the same ground some months later.
He also takes us to West Virginia, an area of Virginia predominantly populated by poor, rural whites who resented the plantation class of the Tidewater and who were prone to support Union interests. A young general by the name of George McClellan waged an energetic and successful campaign to conquer the region held by disorganized, and poorly led, Rebel forces. Nipping off West Virginia threatened the vital Shenandoah Valley, the Virginia rail networks radiating outwards from Charlottesville and Lynchburg, and strategically outflanked a schizophrenic Kentucky who wanted to support both sides, had a conniption, and declared neutrality.
It also put a young McClellan on the national map. Much more heard from him later.
However, the main event was the Federal army advancing south from Washington. Aimed at striking the main Confederate concentration at Manassas, this Union force of some 36,000 men, the largest force yet assembled in North America (soon to be dwarfed by other armies as the war progressed) marched cautiously towards the waiting Rebels.
On 21 July, 1861, the Battle of Manassas/Bull Run ended in a resounding Southern triumph, shocked both sides to it's gruesome casualties (2,000 Rebel, 3,000 Yankee), and forced a change of command in the Federal armies that would alter the strategic direction of the war.
Overall this is a very good volume of this beautiful set. It can easily stand on its own read separately and serves as a very fine primer to the opening of hostilities in the Eastern Theater of the War Between the States.