In a nut shell, the organization of the artillery within both armies during the Civil War evolved from dispersion of artillery pieces within infantry formations to concentration of batteries at higher echelons of command.

During the first two years of the war, commanders believed having cannon in close proximity to the ranks of inexperienced, often unsteady troops was necessary to bolster the soldiers' courage and confidence in battle. While this was undoubtedly the effect, it came at the price of having guns on one part of the battlefield stand idle while the battle raged in another sector. Infantry brigade commanders (brigades = groups of regiments of 1000; regiments = groups of companies of 100) who "owned" these guns were very reluctant to send them where they were needed out of concern that they might need them at any moment as well. It was recognized that the artillery was too powerful and scarce a combat arm to be wasted like this.

The Confederate Army of Northern Virginia acted first. After the Battle of Fredericksburg in December 1862, General Lee assigned battalions of four batteries to division (groups of brigades) and corps (groups of divisions) commanders while retaining one battalion at the army level (group of corps). This pulled the guns off of the firing lines where they could be moved within the division sectors as battles developed, and be reenforced by the corps' artillery in a pinch. It worked like a charm for Lee's army at the Battle of Chancellorsville in May 1863 and beyond.

The overall poor showing of the Union Army of the Potomac's artillery (and practically everything else) at Chancellorsville was the turning point that led General George Meade to approve a reorganization similar to Lee's before the Battle of Gettysburg in July 1863. The resulting improvement in the Union artillery's performance there was a major factor contributing to the Union victory.

The next major battle between these two armies, however, led General Ulysses Grant, now in command of all Union forces, to get rid of a large part of the Army of the Potomac's artillery all together. The Battle of the Wilderness in May 1864 showed him that in the often dense and tangled wooded vegetation of eastern Virginia, artillery was of little use. As this was the region through which he planned on driving towards Richmond, the new artillery organization was largely scraped and the guns were employed piecemeal again.