The Battle of Gettysburg started on this day in 1863. Here are some essays on Gettysburg from MilitaryHistoryOnline. Here is a virtual tour with photos and maps.
"Nothing in the history of the Rebellion has equaled in inhumanity and atrocity the horrid butchery at Fort Pillow, on the 13th of April, 1864. In no other school than slavery could human beings have been trained to such readiness for cruelties like these. Accustomed to brutality and bestiality all their lives, it was easy for them to perpetrate the atrocities which will startle the civilized foreign world, as they have awakened the indignation of our own people."
On December 13, 1862, Sgt. Richard Rowland Kirkland of the 2nd Carolina stood in the Sunken Road at the bottom of Marye's Heights at the Battle of Fredericksburg. The 19-year-old Kirkland was part of Longstreet's First Corps; across from him was Hooker's Center Grand Division, part of the Army of the Potomac under Ambrose Burnside. (More boring history stuff inside.)
A soldier in War. A letter home. Nobody will ever top Sullivan Ballou's. (Youtube Video) A week before the battle of Bull Run, Sullivan Ballou, a major in the 2nd Rhode Island Volunteers, wrote home to his wife in Smithfield. The actual letter begins @ 2:25 into the video. But it's far from a waste to watch the whole six minutes.
The Battle of Glorieta Pass is considered the turning point of the Civil War, in terms of the New Mexico Territory. It happened March 26-28th, 1862. Initially Charles L. Pyron and William Reed Scurry's Confederate force, based at Johnson's Ranch, thought that they had won the battle. They would soon learn that the Union troops, lead by John P. Slough, had circled and destroyed their supplies, leading to Scurry's retreat towards San Antonio. More detailed battle info:  -Some site photos.